]> git.saurik.com Git - apple/xnu.git/blobdiff - bsd/kern/kern_event.c
xnu-4903.241.1.tar.gz
[apple/xnu.git] / bsd / kern / kern_event.c
index 6d72e54a36bf39408de41d22e39d0f7242789ff9..ecffc8db733f40f94d7e8a2f4773ae9da3744f31 100644 (file)
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000-2016 Apple Inc. All rights reserved.
+ * Copyright (c) 2000-2017 Apple Inc. All rights reserved.
  *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
  *
@@ -55,6 +55,7 @@
  *     @(#)kern_event.c       1.0 (3/31/2000)
  */
 #include <stdint.h>
+#include <machine/atomic.h>
 
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/proc_info.h>
 #include <sys/codesign.h>
 #include <sys/pthread_shims.h>
+#include <sys/kdebug.h>
+#include <sys/reason.h>
+#include <os/reason_private.h>
+#include <pexpert/pexpert.h>
 
 #include <kern/locks.h>
 #include <kern/clock.h>
+#include <kern/cpu_data.h>
 #include <kern/policy_internal.h>
 #include <kern/thread_call.h>
 #include <kern/sched_prim.h>
 #include <kern/zalloc.h>
 #include <kern/kalloc.h>
 #include <kern/assert.h>
+#include <kern/ast.h>
+#include <kern/thread.h>
+#include <kern/kcdata.h>
 
+#include <pthread/priority_private.h>
+#include <pthread/workqueue_syscalls.h>
+#include <pthread/workqueue_internal.h>
 #include <libkern/libkern.h>
+#include <libkern/OSAtomic.h>
+
 #include "net/net_str_id.h"
 
 #include <mach/task.h>
+#include <libkern/section_keywords.h>
 
 #if CONFIG_MEMORYSTATUS
 #include <sys/kern_memorystatus.h>
 #endif
 
-/*
- * JMM - this typedef needs to be unified with pthread_priority_t
- *       and mach_msg_priority_t. It also needs to be the same type
- *       everywhere.
- */
-typedef int32_t qos_t;
+extern thread_t        port_name_to_thread(mach_port_name_t    port_name); /* osfmk/kern/ipc_tt.h   */
+extern mach_port_name_t ipc_entry_name_mask(mach_port_name_t name); /* osfmk/ipc/ipc_entry.h */
+
+#define KEV_EVTID(code) BSDDBG_CODE(DBG_BSD_KEVENT, (code))
 
 MALLOC_DEFINE(M_KQUEUE, "kqueue", "memory for kqueue system");
 
 #define        KQ_EVENT        NO_EVENT64
 
-static inline void kqlock(struct kqueue *kq);
-static inline void kqunlock(struct kqueue *kq);
-
-static int kqlock2knoteuse(struct kqueue *kq, struct knote *kn);
-static int kqlock2knotedrop(struct kqueue *kq, struct knote *kn);
-static int kqlock2knotedetach(struct kqueue *kq, struct knote *kn);
-static int knoteuse2kqlock(struct kqueue *kq, struct knote *kn, int defer_drop);
-
 static int kqueue_read(struct fileproc *fp, struct uio *uio,
-    int flags, vfs_context_t ctx);
+               int flags, vfs_context_t ctx);
 static int kqueue_write(struct fileproc *fp, struct uio *uio,
-    int flags, vfs_context_t ctx);
+               int flags, vfs_context_t ctx);
 static int kqueue_ioctl(struct fileproc *fp, u_long com, caddr_t data,
-    vfs_context_t ctx);
+               vfs_context_t ctx);
 static int kqueue_select(struct fileproc *fp, int which, void *wq_link_id,
-    vfs_context_t ctx);
+               vfs_context_t ctx);
 static int kqueue_close(struct fileglob *fg, vfs_context_t ctx);
 static int kqueue_kqfilter(struct fileproc *fp, struct knote *kn,
-       vfs_context_t ctx);
+               struct kevent_internal_s *kev, vfs_context_t ctx);
 static int kqueue_drain(struct fileproc *fp, vfs_context_t ctx);
 
 static const struct fileops kqueueops = {
@@ -146,9 +151,11 @@ static const struct fileops kqueueops = {
        .fo_drain = kqueue_drain,
 };
 
-static int kevent_internal(struct proc *p, int fd, 
+static void kevent_put_kq(struct proc *p, kqueue_id_t id, struct fileproc *fp, struct kqueue *kq);
+static int kevent_internal(struct proc *p,
+                          kqueue_id_t id, kqueue_id_t *id_out,
                           user_addr_t changelist, int nchanges,
-                          user_addr_t eventlist, int nevents, 
+                          user_addr_t eventlist, int nevents,
                           user_addr_t data_out, uint64_t data_available,
                           unsigned int flags, user_addr_t utimeout,
                           kqueue_continue_t continuation,
@@ -159,41 +166,77 @@ static int kevent_copyout(struct kevent_internal_s *kevp, user_addr_t *addrp,
                          struct proc *p, unsigned int flags);
 char * kevent_description(struct kevent_internal_s *kevp, char *s, size_t n);
 
+static int kevent_register_wait_prepare(struct knote *kn, struct kevent_internal_s *kev);
+static void kevent_register_wait_block(struct turnstile *ts, thread_t handoff_thread,
+               struct knote_lock_ctx *knlc, thread_continue_t cont,
+               struct _kevent_register *cont_args) __dead2;
+static void kevent_register_wait_return(struct _kevent_register *cont_args) __dead2;
+static void kevent_register_wait_cleanup(struct knote *kn);
+static inline void kqueue_release_last(struct proc *p, kqueue_t kqu);
 static void kqueue_interrupt(struct kqueue *kq);
 static int kevent_callback(struct kqueue *kq, struct kevent_internal_s *kevp,
-                          void *data);
+               void *data);
 static void kevent_continue(struct kqueue *kq, void *data, int error);
 static void kqueue_scan_continue(void *contp, wait_result_t wait_result);
 static int kqueue_process(struct kqueue *kq, kevent_callback_t callback, void *callback_data,
-                          struct filt_process_s *process_data, kq_index_t servicer_qos_index,
-                          int *countp, struct proc *p);
-static int kqueue_begin_processing(struct kqueue *kq, kq_index_t qos_index, unsigned int flags);
-static void kqueue_end_processing(struct kqueue *kq, kq_index_t qos_index, unsigned int flags);
-static struct kqtailq *kqueue_get_base_queue(struct kqueue *kq, kq_index_t qos_index);
-static struct kqtailq *kqueue_get_high_queue(struct kqueue *kq, kq_index_t qos_index);
+               struct filt_process_s *process_data, int *countp);
 static int kqueue_queue_empty(struct kqueue *kq, kq_index_t qos_index);
 
-static struct kqtailq *kqueue_get_suppressed_queue(struct kqueue *kq, kq_index_t qos_index);
+static struct kqtailq *kqueue_get_suppressed_queue(kqueue_t kq, struct knote *kn);
+static void kqueue_threadreq_initiate(struct kqueue *kq, struct kqrequest *kqr, kq_index_t qos, int flags);
 
-static void kqworkq_request_thread(struct kqworkq *kqwq, kq_index_t qos_index);
-static void kqworkq_request_help(struct kqworkq *kqwq, kq_index_t qos_index, uint32_t type);
-static void kqworkq_update_override(struct kqworkq *kqwq, kq_index_t qos_index, kq_index_t override_index);
-static void kqworkq_bind_thread(struct kqworkq *kqwq, kq_index_t qos_index, thread_t thread, unsigned int flags);
-static void kqworkq_unbind_thread(struct kqworkq *kqwq, kq_index_t qos_index, thread_t thread, unsigned int flags);
+static void kqworkq_update_override(struct kqworkq *kqwq, struct knote *kn, kq_index_t qos);
+static void kqworkq_unbind(proc_t p, struct kqrequest *kqr);
+static thread_qos_t kqworkq_unbind_locked(struct kqworkq *kqwq, struct kqrequest *kqr, thread_t thread);
 static struct kqrequest *kqworkq_get_request(struct kqworkq *kqwq, kq_index_t qos_index);
 
+static void kqworkloop_update_override(struct kqworkloop *kqwl, kq_index_t override_index);
+static void kqworkloop_unbind(proc_t p, struct kqworkloop *kwql);
+static thread_qos_t kqworkloop_unbind_locked(struct kqworkloop *kwql, thread_t thread);
+static kq_index_t kqworkloop_owner_override(struct kqworkloop *kqwl);
+enum {
+       KQWL_UTQ_NONE,
+       /*
+        * The wakeup qos is the qos of QUEUED knotes.
+        *
+        * This QoS is accounted for with the events override in the
+        * kqr_override_index field. It is raised each time a new knote is queued at
+        * a given QoS. The kqr_wakeup_indexes field is a superset of the non empty
+        * knote buckets and is recomputed after each event delivery.
+        */
+       KQWL_UTQ_UPDATE_WAKEUP_QOS,
+       KQWL_UTQ_UPDATE_STAYACTIVE_QOS,
+       KQWL_UTQ_RECOMPUTE_WAKEUP_QOS,
+       KQWL_UTQ_UNBINDING, /* attempt to rebind */
+       KQWL_UTQ_PARKING,
+       /*
+        * The wakeup override is for suppressed knotes that have fired again at
+        * a higher QoS than the one for which they are suppressed already.
+        * This override is cleared when the knote suppressed list becomes empty.
+        */
+       KQWL_UTQ_UPDATE_WAKEUP_OVERRIDE,
+       KQWL_UTQ_RESET_WAKEUP_OVERRIDE,
+       /*
+        * The QoS is the maximum QoS of an event enqueued on this workloop in
+        * userland. It is copied from the only EVFILT_WORKLOOP knote with
+        * a NOTE_WL_THREAD_REQUEST bit set allowed on this workloop. If there is no
+        * such knote, this QoS is 0.
+        */
+       KQWL_UTQ_SET_QOS_INDEX,
+       KQWL_UTQ_REDRIVE_EVENTS,
+};
+static void kqworkloop_update_threads_qos(struct kqworkloop *kqwl, int op, kq_index_t qos);
+static void kqworkloop_request_help(struct kqworkloop *kqwl, kq_index_t qos_index);
+static int kqworkloop_end_processing(struct kqworkloop *kqwl, int flags, int kevent_flags);
 
 static int knote_process(struct knote *kn, kevent_callback_t callback, void *callback_data,
-                        struct filt_process_s *process_data, struct proc *p);
-#if 0
-static void knote_put(struct knote *kn);
-#endif
+                        struct filt_process_s *process_data);
 
-static int knote_fdadd(struct knote *kn, struct proc *p);
-static void knote_fdremove(struct knote *kn, struct proc *p);
-static struct knote *knote_fdfind(struct kqueue *kq, struct kevent_internal_s *kev, struct proc *p);
+static int kq_add_knote(struct kqueue *kq, struct knote *kn,
+               struct knote_lock_ctx *knlc, struct proc *p);
+static struct knote *kq_find_knote_and_kq_lock(struct kqueue *kq, struct kevent_internal_s *kev, bool is_fd, struct proc *p);
 
-static void knote_drop(struct knote *kn, struct proc *p);
+static void knote_drop(struct kqueue *kq, struct knote *kn, struct knote_lock_ctx *knlc);
 static struct knote *knote_alloc(void);
 static void knote_free(struct knote *kn);
 
@@ -210,132 +253,77 @@ static void knote_suppress(struct knote *kn);
 static void knote_unsuppress(struct knote *kn);
 static void knote_wakeup(struct knote *kn);
 
-static kq_index_t knote_get_queue_index(struct knote *kn);
-static struct kqtailq *knote_get_queue(struct knote *kn);
-static struct kqtailq *knote_get_suppressed_queue(struct knote *kn);
-static kq_index_t knote_get_req_index(struct knote *kn);
-static kq_index_t knote_get_qos_index(struct knote *kn);
-static void knote_set_qos_index(struct knote *kn, kq_index_t qos_index);
+static bool knote_should_apply_qos_override(struct kqueue *kq, struct knote *kn,
+               int result, thread_qos_t *qos_out);
+static void knote_apply_qos_override(struct knote *kn, kq_index_t qos_index);
+static void knote_adjust_qos(struct kqueue *kq, struct knote *kn, int result);
+static void knote_reset_priority(struct knote *kn, pthread_priority_t pp);
 static kq_index_t knote_get_qos_override_index(struct knote *kn);
-static void knote_set_qos_override_index(struct knote *kn, kq_index_t qos_index);
-
-static int filt_fileattach(struct knote *kn);
-static struct filterops file_filtops = {
-       .f_isfd = 1,
-       .f_attach = filt_fileattach,
-};
-
-static void filt_kqdetach(struct knote *kn);
-static int filt_kqueue(struct knote *kn, long hint);
-static int filt_kqtouch(struct knote *kn, struct kevent_internal_s *kev);
-static int filt_kqprocess(struct knote *kn, struct filt_process_s *data, struct kevent_internal_s *kev);
-static struct filterops kqread_filtops = {
-       .f_isfd = 1,
-       .f_detach = filt_kqdetach,
-       .f_event = filt_kqueue,
-       .f_touch = filt_kqtouch,
-       .f_process = filt_kqprocess,
-};
-
-/* placeholder for not-yet-implemented filters */
-static int filt_badattach(struct knote *kn);
-static struct filterops bad_filtops = {
-       .f_attach = filt_badattach,
-};
-
-static int filt_procattach(struct knote *kn);
-static void filt_procdetach(struct knote *kn);
-static int filt_proc(struct knote *kn, long hint);
-static int filt_proctouch(struct knote *kn, struct kevent_internal_s *kev);
-static int filt_procprocess(struct knote *kn, struct filt_process_s *data, struct kevent_internal_s *kev);
-static struct filterops proc_filtops = {
-       .f_attach = filt_procattach,
-       .f_detach = filt_procdetach,
-       .f_event = filt_proc,
-       .f_touch = filt_proctouch,
-       .f_process = filt_procprocess,
-};
-
-#if CONFIG_MEMORYSTATUS
-extern struct filterops memorystatus_filtops;
-#endif /* CONFIG_MEMORYSTATUS */
-
-extern struct filterops fs_filtops;
-
-extern struct filterops sig_filtops;
-
-/* Timer filter */
-static int filt_timerattach(struct knote *kn);
-static void filt_timerdetach(struct knote *kn);
-static int filt_timer(struct knote *kn, long hint);
-static int filt_timertouch(struct knote *kn, struct kevent_internal_s *kev);
-static int filt_timerprocess(struct knote *kn, struct filt_process_s *data, struct kevent_internal_s *kev);
-static struct filterops timer_filtops = {
-       .f_attach = filt_timerattach,
-       .f_detach = filt_timerdetach,
-       .f_event = filt_timer,
-       .f_touch = filt_timertouch,
-       .f_process = filt_timerprocess,
-};
-
-/* Helpers */
-static void filt_timerexpire(void *knx, void *param1);
-static int filt_timervalidate(struct knote *kn);
-static void filt_timerupdate(struct knote *kn, int num_fired);
-static void filt_timercancel(struct knote *kn);
-
-#define        TIMER_RUNNING           0x1
-#define        TIMER_CANCELWAIT        0x2
-
-static lck_mtx_t _filt_timerlock;
-static void filt_timerlock(void);
-static void filt_timerunlock(void);
+static void knote_set_qos_overcommit(struct knote *kn);
 
 static zone_t knote_zone;
 static zone_t kqfile_zone;
 static zone_t kqworkq_zone;
+static zone_t kqworkloop_zone;
+#if DEVELOPMENT || DEBUG
+#define KEVENT_PANIC_ON_WORKLOOP_OWNERSHIP_LEAK  (1U << 0)
+#define KEVENT_PANIC_ON_NON_ENQUEUED_PROCESS     (1U << 1)
+#define KEVENT_PANIC_BOOT_ARG_INITIALIZED        (1U << 31)
+
+#define KEVENT_PANIC_DEFAULT_VALUE (0)
+static uint32_t
+kevent_debug_flags(void)
+{
+       static uint32_t flags = KEVENT_PANIC_DEFAULT_VALUE;
+
+       if ((flags & KEVENT_PANIC_BOOT_ARG_INITIALIZED) == 0) {
+               uint32_t value = 0;
+               if (!PE_parse_boot_argn("kevent_debug", &value, sizeof(value))) {
+                       value = KEVENT_PANIC_DEFAULT_VALUE;
+               }
+               value |= KEVENT_PANIC_BOOT_ARG_INITIALIZED;
+               os_atomic_store(&flags, value, relaxed);
+       }
+       return flags;
+}
+#endif
 
 #define        KN_HASH(val, mask)      (((val) ^ (val >> 8)) & (mask))
 
-#if 0
-extern struct filterops aio_filtops;
-#endif
-
-/* Mach portset filter */
-extern struct filterops machport_filtops;
-
-/* User filter */
-static int filt_userattach(struct knote *kn);
-static void filt_userdetach(struct knote *kn);
-static int filt_user(struct knote *kn, long hint);
-static int filt_usertouch(struct knote *kn, struct kevent_internal_s *kev);
-static int filt_userprocess(struct knote *kn, struct filt_process_s *data, struct kevent_internal_s *kev);
-static struct filterops user_filtops = {
-       .f_attach = filt_userattach,
-       .f_detach = filt_userdetach,
-       .f_event = filt_user,
-       .f_touch = filt_usertouch,
-       .f_process = filt_userprocess,
+/* placeholder for not-yet-implemented filters */
+static int filt_badattach(struct knote *kn, struct kevent_internal_s *kev);
+static int filt_badevent(struct knote *kn, long hint);
+SECURITY_READ_ONLY_EARLY(static struct filterops) bad_filtops = {
+       .f_attach = filt_badattach,
 };
 
-static lck_spin_t _filt_userlock;
-static void filt_userlock(void);
-static void filt_userunlock(void);
-
-extern struct filterops pipe_rfiltops;
-extern struct filterops pipe_wfiltops;
-extern struct filterops ptsd_kqops;
-extern struct filterops soread_filtops;
-extern struct filterops sowrite_filtops;
-extern struct filterops sock_filtops;
-extern struct filterops soexcept_filtops;
-extern struct filterops spec_filtops;
-extern struct filterops bpfread_filtops;
-extern struct filterops necp_fd_rfiltops;
-extern struct filterops skywalk_channel_rfiltops;
-extern struct filterops skywalk_channel_wfiltops;
-extern struct filterops fsevent_filtops;
-extern struct filterops vnode_filtops;
+#if CONFIG_MEMORYSTATUS
+extern const struct filterops memorystatus_filtops;
+#endif /* CONFIG_MEMORYSTATUS */
+extern const struct filterops fs_filtops;
+extern const struct filterops sig_filtops;
+extern const struct filterops machport_filtops;
+extern const struct filterops pipe_rfiltops;
+extern const struct filterops pipe_wfiltops;
+extern const struct filterops ptsd_kqops;
+extern const struct filterops ptmx_kqops;
+extern const struct filterops soread_filtops;
+extern const struct filterops sowrite_filtops;
+extern const struct filterops sock_filtops;
+extern const struct filterops soexcept_filtops;
+extern const struct filterops spec_filtops;
+extern const struct filterops bpfread_filtops;
+extern const struct filterops necp_fd_rfiltops;
+extern const struct filterops fsevent_filtops;
+extern const struct filterops vnode_filtops;
+extern const struct filterops tty_filtops;
+
+const static struct filterops file_filtops;
+const static struct filterops kqread_filtops;
+const static struct filterops proc_filtops;
+const static struct filterops timer_filtops;
+const static struct filterops user_filtops;
+const static struct filterops workloop_filtops;
 
 /*
  *
@@ -344,138 +332,93 @@ extern struct filterops vnode_filtops;
  * - Add a new "EVFILT_" option value to bsd/sys/event.h (typically a negative value)
  *   in the exported section of the header
  * - Update the EVFILT_SYSCOUNT value to reflect the new addition
- * - Add a filterops to the sysfilt_ops array. Public filters should be added at the end 
+ * - Add a filterops to the sysfilt_ops array. Public filters should be added at the end
  *   of the Public Filters section in the array.
  * Private filters:
  * - Add a new "EVFILT_" value to bsd/sys/event.h (typically a positive value)
  *   in the XNU_KERNEL_PRIVATE section of the header
  * - Update the EVFILTID_MAX value to reflect the new addition
- * - Add a filterops to the sysfilt_ops. Private filters should be added at the end of 
- *   the Private filters section of the array. 
+ * - Add a filterops to the sysfilt_ops. Private filters should be added at the end of
+ *   the Private filters section of the array.
  */
-static struct filterops *sysfilt_ops[EVFILTID_MAX] = {
+SECURITY_READ_ONLY_EARLY(static struct filterops *) sysfilt_ops[EVFILTID_MAX] = {
        /* Public Filters */
-       [~EVFILT_READ]                                  = &file_filtops,
-       [~EVFILT_WRITE]                                 = &file_filtops,
-       [~EVFILT_AIO]                                   = &bad_filtops,
-       [~EVFILT_VNODE]                                 = &file_filtops,
-       [~EVFILT_PROC]                                  = &proc_filtops,
-       [~EVFILT_SIGNAL]                                = &sig_filtops,
-       [~EVFILT_TIMER]                                 = &timer_filtops,
-       [~EVFILT_MACHPORT]                              = &machport_filtops,
-       [~EVFILT_FS]                                    = &fs_filtops,
-       [~EVFILT_USER]                                  = &user_filtops,
-                                                                         &bad_filtops,
-                                                                         &bad_filtops,
-       [~EVFILT_SOCK]                                  = &file_filtops,
+       [~EVFILT_READ]                  = &file_filtops,
+       [~EVFILT_WRITE]                 = &file_filtops,
+       [~EVFILT_AIO]                   = &bad_filtops,
+       [~EVFILT_VNODE]                 = &file_filtops,
+       [~EVFILT_PROC]                  = &proc_filtops,
+       [~EVFILT_SIGNAL]                = &sig_filtops,
+       [~EVFILT_TIMER]                 = &timer_filtops,
+       [~EVFILT_MACHPORT]              = &machport_filtops,
+       [~EVFILT_FS]                    = &fs_filtops,
+       [~EVFILT_USER]                  = &user_filtops,
+                                         &bad_filtops,
+       [~EVFILT_VM]                    = &bad_filtops,
+       [~EVFILT_SOCK]                  = &file_filtops,
 #if CONFIG_MEMORYSTATUS
-       [~EVFILT_MEMORYSTATUS]                  = &memorystatus_filtops,
+       [~EVFILT_MEMORYSTATUS]          = &memorystatus_filtops,
 #else
-       [~EVFILT_MEMORYSTATUS]                  = &bad_filtops,
+       [~EVFILT_MEMORYSTATUS]          = &bad_filtops,
 #endif
-       [~EVFILT_EXCEPT]                                = &file_filtops,
+       [~EVFILT_EXCEPT]                = &file_filtops,
+       [~EVFILT_WORKLOOP]              = &workloop_filtops,
 
        /* Private filters */
-       [EVFILTID_KQREAD]                               = &kqread_filtops,
-       [EVFILTID_PIPE_R]                               = &pipe_rfiltops,
-       [EVFILTID_PIPE_W]                               = &pipe_wfiltops,
-       [EVFILTID_PTSD]                                 = &ptsd_kqops,
-       [EVFILTID_SOREAD]                               = &soread_filtops,
-       [EVFILTID_SOWRITE]                              = &sowrite_filtops,
-       [EVFILTID_SCK]                                  = &sock_filtops,
-       [EVFILTID_SOEXCEPT]                     = &soexcept_filtops,
-       [EVFILTID_SPEC]                                 = &spec_filtops,
-       [EVFILTID_BPFREAD]                              = &bpfread_filtops,
-       [EVFILTID_NECP_FD]                              = &necp_fd_rfiltops,
-       [EVFILTID_FSEVENT]                              = &fsevent_filtops,
-       [EVFILTID_VN]                                   = &vnode_filtops
+       [EVFILTID_KQREAD]               = &kqread_filtops,
+       [EVFILTID_PIPE_R]               = &pipe_rfiltops,
+       [EVFILTID_PIPE_W]               = &pipe_wfiltops,
+       [EVFILTID_PTSD]                 = &ptsd_kqops,
+       [EVFILTID_SOREAD]               = &soread_filtops,
+       [EVFILTID_SOWRITE]              = &sowrite_filtops,
+       [EVFILTID_SCK]                  = &sock_filtops,
+       [EVFILTID_SOEXCEPT]             = &soexcept_filtops,
+       [EVFILTID_SPEC]                 = &spec_filtops,
+       [EVFILTID_BPFREAD]              = &bpfread_filtops,
+       [EVFILTID_NECP_FD]              = &necp_fd_rfiltops,
+       [EVFILTID_FSEVENT]              = &fsevent_filtops,
+       [EVFILTID_VN]                   = &vnode_filtops,
+       [EVFILTID_TTY]                  = &tty_filtops,
+       [EVFILTID_PTMX]                 = &ptmx_kqops,
 };
 
 /* waitq prepost callback */
 void waitq_set__CALLING_PREPOST_HOOK__(void *kq_hook, void *knote_hook, int qos);
 
-#ifndef _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG
-#define _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG 0x02000000 /* pthread event manager bit */
-#endif
-#ifndef _PTHREAD_PRIORITY_OVERCOMMIT_FLAG
-#define _PTHREAD_PRIORITY_OVERCOMMIT_FLAG    0x80000000 /* request overcommit threads */
-#endif
-#ifndef _PTHREAD_PRIORITY_QOS_CLASS_MASK
-#define _PTHREAD_PRIORITY_QOS_CLASS_MASK    0x003fff00  /* QoS class mask */
-#endif
-#ifndef _PTHREAD_PRIORITY_QOS_CLASS_SHIFT_32
-#define _PTHREAD_PRIORITY_QOS_CLASS_SHIFT_32 8
-#endif
-
-static inline
-qos_t canonicalize_kevent_qos(qos_t qos)
-{
-       unsigned long canonical;
-
-       /* preserve manager and overcommit flags in this case */
-       canonical = pthread_priority_canonicalize(qos, FALSE);
-       return (qos_t)canonical;
-}
-
-static inline
-kq_index_t qos_index_from_qos(qos_t qos, boolean_t propagation)
+static inline struct kqworkloop *
+kqr_kqworkloop(struct kqrequest *kqr)
 {
-       kq_index_t qos_index;
-       unsigned long flags = 0;
-
-       qos_index = (kq_index_t)thread_qos_from_pthread_priority(
-                               (unsigned long)qos, &flags);
-       
-       if (!propagation && (flags & _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG))
-               return KQWQ_QOS_MANAGER;
-
-       return qos_index;
+       if (kqr->kqr_state & KQR_WORKLOOP) {
+               return __container_of(kqr, struct kqworkloop, kqwl_request);
+       }
+       return NULL;
 }
 
-static inline
-qos_t qos_from_qos_index(kq_index_t qos_index)
+static inline kqueue_t
+kqr_kqueue(proc_t p, struct kqrequest *kqr)
 {
-       if (qos_index == KQWQ_QOS_MANAGER)
-               return  _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
-
-       if (qos_index == 0)
-               return 0; /* Unspecified */
-
-       /* Should have support from pthread kext support */
-       return (1 << (qos_index - 1 + 
-                     _PTHREAD_PRIORITY_QOS_CLASS_SHIFT_32));
+       kqueue_t kqu;
+       if (kqr->kqr_state & KQR_WORKLOOP) {
+               kqu.kqwl = kqr_kqworkloop(kqr);
+       } else {
+               kqu.kqwq = (struct kqworkq *)p->p_fd->fd_wqkqueue;
+               assert(kqr >= kqu.kqwq->kqwq_request &&
+                               kqr < kqu.kqwq->kqwq_request + KQWQ_NBUCKETS);
+       }
+       return kqu;
 }
 
-static inline
-kq_index_t qos_index_for_servicer(int qos_class, thread_t thread, int flags)
+static inline boolean_t
+is_workqueue_thread(thread_t thread)
 {
-       kq_index_t qos_index;
-
-       if (flags & KEVENT_FLAG_WORKQ_MANAGER)
-               return KQWQ_QOS_MANAGER;
-
-       /* 
-        * If the caller didn't pass in a class (legacy pthread kext)
-        * the we use the thread policy QoS of the current thread.
-        */
-       assert(qos_class != -1);
-       if (qos_class == -1)
-               qos_index = proc_get_thread_policy(thread,
-                                                  TASK_POLICY_ATTRIBUTE,
-                                                  TASK_POLICY_QOS);
-       else
-               qos_index = (kq_index_t)qos_class;
-
-       assert(qos_index > 0 && qos_index < KQWQ_NQOS);
-
-       return qos_index;
+       return (thread_get_tag(thread) & THREAD_TAG_WORKQUEUE);
 }
 
 /*
  * kqueue/note lock implementations
  *
  *     The kqueue lock guards the kq state, the state of its queues,
- *     and the kqueue-aware status and use counts of individual knotes.
+ *     and the kqueue-aware status and locks of individual knotes.
  *
  *     The kqueue workq lock is used to protect state guarding the
  *     interaction of the kqueue with the workq.  This state cannot
@@ -489,236 +432,365 @@ kq_index_t qos_index_for_servicer(int qos_class, thread_t thread, int flags)
  *     by calling the filter to get a [consistent] snapshot of that
  *     data.
  */
-lck_grp_attr_t * kq_lck_grp_attr;
-lck_grp_t * kq_lck_grp;
-lck_attr_t * kq_lck_attr;
+static lck_grp_attr_t *kq_lck_grp_attr;
+static lck_grp_t *kq_lck_grp;
+static lck_attr_t *kq_lck_attr;
 
 static inline void
-kqlock(struct kqueue *kq)
+kqlock(kqueue_t kqu)
 {
-       lck_spin_lock(&kq->kq_lock);
+       lck_spin_lock(&kqu.kq->kq_lock);
 }
 
 static inline void
-kqunlock(struct kqueue *kq)
+kqlock_held(__assert_only kqueue_t kqu)
 {
-       lck_spin_unlock(&kq->kq_lock);
+       LCK_SPIN_ASSERT(&kqu.kq->kq_lock, LCK_ASSERT_OWNED);
 }
 
+static inline void
+kqunlock(kqueue_t kqu)
+{
+       lck_spin_unlock(&kqu.kq->kq_lock);
+}
 
-/*
- * Convert a kq lock to a knote use referece.
- *
- *     If the knote is being dropped, or has
- *  vanished, we can't get a use reference.
- *  Just return with it still locked.
- *
- *     - kq locked at entry
- *     - unlock on exit if we get the use reference
- */
-static int
-kqlock2knoteuse(struct kqueue *kq, struct knote *kn)
+static inline void
+kq_req_lock(kqueue_t kqu)
 {
-       if (kn->kn_status & (KN_DROPPING | KN_VANISHED))
-               return (0);
+       assert(kqu.kq->kq_state & (KQ_WORKLOOP | KQ_WORKQ));
+       lck_spin_lock(&kqu.kq->kq_reqlock);
+}
 
-       assert(kn->kn_status & KN_ATTACHED);
-       kn->kn_inuse++;
-       kqunlock(kq);
-       return (1);
+static inline void
+kq_req_unlock(kqueue_t kqu)
+{
+       assert(kqu.kq->kq_state & (KQ_WORKLOOP | KQ_WORKQ));
+       lck_spin_unlock(&kqu.kq->kq_reqlock);
+}
+
+static inline void
+kq_req_held(__assert_only kqueue_t kqu)
+{
+       assert(kqu.kq->kq_state & (KQ_WORKLOOP | KQ_WORKQ));
+       LCK_SPIN_ASSERT(&kqu.kq->kq_reqlock, LCK_ASSERT_OWNED);
+}
+
+static inline void
+knhash_lock(proc_t p)
+{
+       lck_mtx_lock(&p->p_fd->fd_knhashlock);
+}
+
+static inline void
+knhash_unlock(proc_t p)
+{
+       lck_mtx_unlock(&p->p_fd->fd_knhashlock);
 }
 
+#pragma mark knote locks
 
 /*
- * Convert from a knote use reference back to kq lock.
+ * Enum used by the knote_lock_* functions.
  *
- *     Drop a use reference and wake any waiters if
- *     this is the last one.
+ * KNOTE_KQ_LOCK_ALWAYS
+ *   The function will always return with the kq lock held.
  *
- *  If someone is trying to drop the knote, but the
- *  caller has events they must deliver, take 
- *  responsibility for the drop later - and wake the
- *  other attempted dropper in a manner that informs
- *  him of the transfer of responsibility.
+ * KNOTE_KQ_UNLOCK_ON_SUCCESS
+ *   The function will return with the kq lock held if it was successful
+ *   (knote_lock() is the only function that can fail).
  *
- *     The exit return indicates if the knote is still alive
- *  (or if not, the other dropper has been given the green
- *  light to drop it).
+ * KNOTE_KQ_UNLOCK_ON_FAILURE
+ *   The function will return with the kq lock held if it was unsuccessful
+ *   (knote_lock() is the only function that can fail).
  *
- *  The kqueue lock is re-taken unconditionally.
+ * KNOTE_KQ_UNLOCK:
+ *   The function returns with the kq unlocked.
  */
-static int
-knoteuse2kqlock(struct kqueue *kq, struct knote *kn, int steal_drop)
+#define KNOTE_KQ_LOCK_ALWAYS      0x0
+#define KNOTE_KQ_LOCK_ON_SUCCESS  0x1
+#define KNOTE_KQ_LOCK_ON_FAILURE  0x2
+#define KNOTE_KQ_UNLOCK           0x3
+
+#if DEBUG || DEVELOPMENT
+__attribute__((noinline, not_tail_called, disable_tail_calls))
+void knote_lock_ctx_chk(struct knote_lock_ctx *knlc)
 {
-       int dropped = 0;
+       /* evil hackery to make sure no one forgets to unlock */
+       assert(knlc->knlc_state == KNOTE_LOCK_CTX_UNLOCKED);
+}
+#endif
 
-       kqlock(kq);
-       if (--kn->kn_inuse == 0) {
+static struct knote_lock_ctx *
+knote_lock_ctx_find(struct kqueue *kq, struct knote *kn)
+{
+       struct knote_lock_ctx *ctx;
+       LIST_FOREACH(ctx, &kq->kq_knlocks, knlc_le) {
+               if (ctx->knlc_knote == kn) return ctx;
+       }
+       panic("knote lock context not found: %p", kn);
+       __builtin_trap();
+}
 
-               if ((kn->kn_status & KN_ATTACHING) != 0) {
-                       kn->kn_status &= ~KN_ATTACHING;
-               }
+/* slowpath of knote_lock() */
+__attribute__((noinline))
+static bool __result_use_check
+knote_lock_slow(struct kqueue *kq, struct knote *kn,
+               struct knote_lock_ctx *knlc, int kqlocking)
+{
+       kqlock_held(kq);
 
-               if ((kn->kn_status & KN_USEWAIT) != 0) {
-                       wait_result_t result;
+       struct knote_lock_ctx *owner_lc = knote_lock_ctx_find(kq, kn);
+       thread_t owner_thread = owner_lc->knlc_thread;
 
-                       /* If we need to, try and steal the drop */
-                       if (kn->kn_status & KN_DROPPING) {
-                               if (steal_drop && !(kn->kn_status & KN_STOLENDROP)) {
-                                       kn->kn_status |= KN_STOLENDROP;
-                               } else {
-                                       dropped = 1;
-                               }
-                       }
+#if DEBUG || DEVELOPMENT
+       knlc->knlc_state = KNOTE_LOCK_CTX_WAITING;
+#endif
 
-                       /* wakeup indicating if ANY USE stole the drop */
-                       result = (kn->kn_status & KN_STOLENDROP) ?
-                                THREAD_RESTART : THREAD_AWAKENED;
+       thread_reference(owner_thread);
+       TAILQ_INSERT_TAIL(&owner_lc->knlc_head, knlc, knlc_tqe);
+       assert_wait(&kn->kn_status, THREAD_UNINT | THREAD_WAIT_NOREPORT);
+       kqunlock(kq);
 
-                       kn->kn_status &= ~KN_USEWAIT;
-                       waitq_wakeup64_all((struct waitq *)&kq->kq_wqs,
-                                          CAST_EVENT64_T(&kn->kn_status),
-                                          result,
-                                          WAITQ_ALL_PRIORITIES);
-               } else {
-                       /* should have seen use-wait if dropping with use refs */
-                       assert((kn->kn_status & (KN_DROPPING|KN_STOLENDROP)) == 0);
+       if (thread_handoff_deallocate(owner_thread) == THREAD_RESTART) {
+               if (kqlocking == KNOTE_KQ_LOCK_ALWAYS ||
+                               kqlocking == KNOTE_KQ_LOCK_ON_FAILURE) {
+                       kqlock(kq);
                }
+#if DEBUG || DEVELOPMENT
+               assert(knlc->knlc_state == KNOTE_LOCK_CTX_WAITING);
+               knlc->knlc_state = KNOTE_LOCK_CTX_UNLOCKED;
+#endif
+               return false;
+       }
+#if DEBUG || DEVELOPMENT
+               assert(knlc->knlc_state == KNOTE_LOCK_CTX_LOCKED);
+#endif
+       if (kqlocking == KNOTE_KQ_LOCK_ALWAYS ||
+                       kqlocking == KNOTE_KQ_LOCK_ON_SUCCESS) {
+               kqlock(kq);
+       }
+       return true;
+}
 
-       } else if (kn->kn_status & KN_DROPPING) {
-               /* not the last ref but want to steal a drop if present */
-               if (steal_drop && ((kn->kn_status & KN_STOLENDROP) == 0)) {
-                       kn->kn_status |= KN_STOLENDROP;
+/*
+ * Attempts to take the "knote" lock.
+ *
+ * Called with the kqueue lock held.
+ *
+ * Returns true if the knote lock is acquired, false if it has been dropped
+ */
+static bool __result_use_check
+knote_lock(struct kqueue *kq, struct knote *kn, struct knote_lock_ctx *knlc,
+               int kqlocking)
+{
+       kqlock_held(kq);
 
-                       /* but we now have to wait to be the last ref */
-                       kn->kn_status |= KN_USEWAIT;
-                       waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
-                                           CAST_EVENT64_T(&kn->kn_status),
-                                           THREAD_UNINT, TIMEOUT_WAIT_FOREVER);
-                       kqunlock(kq);
-                       thread_block(THREAD_CONTINUE_NULL);
-                       kqlock(kq);
-               } else {
-                       dropped = 1;
-               }
+#if DEBUG || DEVELOPMENT
+       assert(knlc->knlc_state == KNOTE_LOCK_CTX_UNLOCKED);
+#endif
+       knlc->knlc_knote = kn;
+       knlc->knlc_thread = current_thread();
+       TAILQ_INIT(&knlc->knlc_head);
+
+       if (__improbable(kn->kn_status & KN_LOCKED)) {
+               return knote_lock_slow(kq, kn, knlc, kqlocking);
        }
 
-       return (!dropped);
+       /*
+        * When the knote will be dropped, the knote lock is taken before
+        * KN_DROPPING is set, and then the knote will be removed from any
+        * hash table that references it before the lock is canceled.
+        */
+       assert((kn->kn_status & KN_DROPPING) == 0);
+       LIST_INSERT_HEAD(&kq->kq_knlocks, knlc, knlc_le);
+       kn->kn_status |= KN_LOCKED;
+#if DEBUG || DEVELOPMENT
+       knlc->knlc_state = KNOTE_LOCK_CTX_LOCKED;
+#endif
+
+       if (kqlocking == KNOTE_KQ_UNLOCK ||
+                       kqlocking == KNOTE_KQ_LOCK_ON_FAILURE) {
+               kqunlock(kq);
+       }
+       return true;
 }
 
 /*
- * Convert a kq lock to a knote use reference
- * (for the purpose of detaching AND vanishing it).
- *
- *     If the knote is being dropped, we can't get
- *     a detach reference, so wait for the knote to
- *  finish dropping before returning.
+ * Unlocks a knote successfully locked with knote_lock().
  *
- *  If the knote is being used for other purposes,
- *  we cannot detach it until those uses are done
- *  as well. Again, just wait for them to finish
- *  (caller will start over at lookup).
+ * Called with the kqueue lock held.
  *
- *     - kq locked at entry
- *     - unlocked on exit 
+ * Returns with the kqueue lock held according to KNOTE_KQ_* flags
  */
-static int
-kqlock2knotedetach(struct kqueue *kq, struct knote *kn)
+static void
+knote_unlock(struct kqueue *kq, struct knote *kn,
+               struct knote_lock_ctx *knlc, int flags)
 {
-       if ((kn->kn_status & KN_DROPPING) || kn->kn_inuse) {
-               /* have to wait for dropper or current uses to go away */
-               kn->kn_status |= KN_USEWAIT;
-               waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
-                                   CAST_EVENT64_T(&kn->kn_status),
-                                   THREAD_UNINT, TIMEOUT_WAIT_FOREVER);
+       kqlock_held(kq);
+
+       assert(knlc->knlc_knote == kn);
+       assert(kn->kn_status & KN_LOCKED);
+#if DEBUG || DEVELOPMENT
+       assert(knlc->knlc_state == KNOTE_LOCK_CTX_LOCKED);
+#endif
+
+       struct knote_lock_ctx *next_owner_lc = TAILQ_FIRST(&knlc->knlc_head);
+
+       LIST_REMOVE(knlc, knlc_le);
+
+       if (next_owner_lc) {
+               assert(next_owner_lc->knlc_knote == kn);
+               TAILQ_REMOVE(&knlc->knlc_head, next_owner_lc, knlc_tqe);
+
+               assert(TAILQ_EMPTY(&next_owner_lc->knlc_head));
+               TAILQ_CONCAT(&next_owner_lc->knlc_head, &knlc->knlc_head, knlc_tqe);
+               LIST_INSERT_HEAD(&kq->kq_knlocks, next_owner_lc, knlc_le);
+#if DEBUG || DEVELOPMENT
+               next_owner_lc->knlc_state = KNOTE_LOCK_CTX_LOCKED;
+#endif
+       } else {
+               kn->kn_status &= ~KN_LOCKED;
+       }
+       if (kn->kn_inuse == 0) {
+               /*
+                * No f_event() in flight anymore, we can leave QoS "Merge" mode
+                *
+                * See knote_should_apply_qos_override()
+                */
+               kn->kn_status &= ~KN_MERGE_QOS;
+       }
+       if (flags & KNOTE_KQ_UNLOCK) {
                kqunlock(kq);
-               thread_block(THREAD_CONTINUE_NULL);
-               return (0);
        }
-       assert((kn->kn_status & KN_VANISHED) == 0);
-       assert(kn->kn_status & KN_ATTACHED);
-       kn->kn_status &= ~KN_ATTACHED;
-       kn->kn_status |= KN_VANISHED;
-       kn->kn_inuse++;
-       kqunlock(kq);
-       return (1);
+       if (next_owner_lc) {
+               thread_wakeup_thread(&kn->kn_status, next_owner_lc->knlc_thread);
+       }
+#if DEBUG || DEVELOPMENT
+       knlc->knlc_state = KNOTE_LOCK_CTX_UNLOCKED;
+#endif
 }
 
 /*
- * Convert a kq lock to a knote drop reference.
+ * Aborts all waiters for a knote lock, and unlock the knote.
  *
- *     If the knote is in use, wait for the use count
- *     to subside.  We first mark our intention to drop
- *     it - keeping other users from "piling on."
- *     If we are too late, we have to wait for the
- *     other drop to complete.
+ * Called with the kqueue lock held.
  *
- *     - kq locked at entry
- *     - always unlocked on exit.
- *     - caller can't hold any locks that would prevent
- *       the other dropper from completing.
+ * Returns with the kqueue lock held according to KNOTE_KQ_* flags
  */
-static int
-kqlock2knotedrop(struct kqueue *kq, struct knote *kn)
+static void
+knote_unlock_cancel(struct kqueue *kq, struct knote *kn,
+               struct knote_lock_ctx *knlc, int kqlocking)
 {
-       int oktodrop;
-       wait_result_t result;
+       kqlock_held(kq);
 
-       oktodrop = ((kn->kn_status & (KN_DROPPING | KN_ATTACHING)) == 0);
-       /* if another thread is attaching, they will become the dropping thread */
-       kn->kn_status |= KN_DROPPING;
-       knote_unsuppress(kn);
-       knote_dequeue(kn);
-       if (oktodrop) {
-               if (kn->kn_inuse == 0) {
-                       kqunlock(kq);
-                       return (oktodrop);
-               }
+       assert(knlc->knlc_knote == kn);
+       assert(kn->kn_status & KN_LOCKED);
+       assert(kn->kn_status & KN_DROPPING);
+
+       LIST_REMOVE(knlc, knlc_le);
+       kn->kn_status &= ~KN_LOCKED;
+
+       if (kqlocking == KNOTE_KQ_UNLOCK ||
+                       kqlocking == KNOTE_KQ_LOCK_ON_FAILURE) {
+               kqunlock(kq);
        }
-       kn->kn_status |= KN_USEWAIT;
-       waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
-                           CAST_EVENT64_T(&kn->kn_status),
-                           THREAD_UNINT, TIMEOUT_WAIT_FOREVER);
-       kqunlock(kq);
-       result = thread_block(THREAD_CONTINUE_NULL);
-       /* THREAD_RESTART == another thread stole the knote drop */
-       return (result == THREAD_AWAKENED);
+       if (!TAILQ_EMPTY(&knlc->knlc_head)) {
+               thread_wakeup_with_result(&kn->kn_status, THREAD_RESTART);
+       }
+#if DEBUG || DEVELOPMENT
+       knlc->knlc_state = KNOTE_LOCK_CTX_UNLOCKED;
+#endif
 }
 
-#if 0
 /*
- * Release a knote use count reference.
+ * Call the f_event hook of a given filter.
+ *
+ * Takes a use count to protect against concurrent drops.
  */
 static void
-knote_put(struct knote *kn)
+knote_call_filter_event(struct kqueue *kq, struct knote *kn, long hint)
 {
-       struct kqueue *kq = knote_get_kq(kn);
+       int result, dropping = 0;
+
+       kqlock_held(kq);
+
+       if (kn->kn_status & (KN_DROPPING | KN_VANISHED))
+               return;
 
+       kn->kn_inuse++;
+       kqunlock(kq);
+       result = filter_call(knote_fops(kn), f_event(kn, hint));
        kqlock(kq);
+
+       dropping = (kn->kn_status & KN_DROPPING);
+
+       if (!dropping && (result & FILTER_ACTIVE)) {
+               if (result & FILTER_ADJUST_EVENT_QOS_BIT)
+                       knote_adjust_qos(kq, kn, result);
+               knote_activate(kn);
+       }
+
        if (--kn->kn_inuse == 0) {
-               if ((kn->kn_status & KN_USEWAIT) != 0) {
-                       kn->kn_status &= ~KN_USEWAIT;
+               if ((kn->kn_status & KN_LOCKED) == 0) {
+                       /*
+                        * We're the last f_event() call and there's no other f_* call in
+                        * flight, we can leave QoS "Merge" mode.
+                        *
+                        * See knote_should_apply_qos_override()
+                        */
+                       kn->kn_status &= ~KN_MERGE_QOS;
+               }
+               if (dropping) {
                        waitq_wakeup64_all((struct waitq *)&kq->kq_wqs,
-                                          CAST_EVENT64_T(&kn->kn_status),
-                                          THREAD_AWAKENED,
-                                          WAITQ_ALL_PRIORITIES);
+                                       CAST_EVENT64_T(&kn->kn_inuse),
+                                       THREAD_AWAKENED, WAITQ_ALL_PRIORITIES);
                }
        }
+}
+
+/*
+ * Called by knote_drop() to wait for the last f_event() caller to be done.
+ *
+ *     - kq locked at entry
+ *     - kq unlocked at exit
+ */
+static void
+knote_wait_for_filter_events(struct kqueue *kq, struct knote *kn)
+{
+       wait_result_t wr = THREAD_NOT_WAITING;
+
+       kqlock_held(kq);
+
+       assert(kn->kn_status & KN_DROPPING);
+
+       if (kn->kn_inuse) {
+               wr = waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
+                               CAST_EVENT64_T(&kn->kn_inuse),
+                               THREAD_UNINT | THREAD_WAIT_NOREPORT, TIMEOUT_WAIT_FOREVER);
+       }
        kqunlock(kq);
+       if (wr == THREAD_WAITING) {
+               thread_block(THREAD_CONTINUE_NULL);
+       }
 }
-#endif
+
+#pragma mark file_filtops
 
 static int
-filt_fileattach(struct knote *kn)
+filt_fileattach(struct knote *kn, struct kevent_internal_s *kev)
 {
-       return (fo_kqfilter(kn->kn_fp, kn, vfs_context_current()));
+       return fo_kqfilter(kn->kn_fp, kn, kev, vfs_context_current());
 }
 
+SECURITY_READ_ONLY_EARLY(static struct filterops) file_filtops = {
+       .f_isfd = 1,
+       .f_attach = filt_fileattach,
+};
+
+#pragma mark kqread_filtops
+
 #define        f_flag f_fglob->fg_flag
-#define        f_msgcount f_fglob->fg_msgcount
-#define        f_cred f_fglob->fg_cred
 #define        f_ops f_fglob->fg_ops
-#define        f_offset f_fglob->fg_offset
 #define        f_data f_fglob->fg_data
 
 static void
@@ -732,15 +804,12 @@ filt_kqdetach(struct knote *kn)
        kqunlock(kq);
 }
 
-/*ARGSUSED*/
 static int
 filt_kqueue(struct knote *kn, __unused long hint)
 {
        struct kqueue *kq = (struct kqueue *)kn->kn_fp->f_data;
-       int count;
 
-       count = kq->kq_count;
-       return (count > 0);
+       return (kq->kq_count > 0);
 }
 
 static int
@@ -752,8 +821,6 @@ filt_kqtouch(struct knote *kn, struct kevent_internal_s *kev)
 
        kqlock(kq);
        kn->kn_data = kq->kq_count;
-       if ((kn->kn_status & KN_UDATA_SPECIFIC) == 0)
-               kn->kn_udata = kev->udata;
        res = (kn->kn_data > 0);
 
        kqunlock(kq);
@@ -781,23 +848,31 @@ filt_kqprocess(struct knote *kn, struct filt_process_s *data, struct kevent_inte
        return res;
 }
 
+SECURITY_READ_ONLY_EARLY(static struct filterops) kqread_filtops = {
+       .f_isfd = 1,
+       .f_detach = filt_kqdetach,
+       .f_event = filt_kqueue,
+       .f_touch = filt_kqtouch,
+       .f_process = filt_kqprocess,
+};
+
+#pragma mark proc_filtops
+
 static int
-filt_procattach(struct knote *kn)
+filt_procattach(struct knote *kn, __unused struct kevent_internal_s *kev)
 {
        struct proc *p;
 
        assert(PID_MAX < NOTE_PDATAMASK);
 
        if ((kn->kn_sfflags & (NOTE_TRACK | NOTE_TRACKERR | NOTE_CHILD)) != 0) {
-               kn->kn_flags = EV_ERROR;
-               kn->kn_data = ENOTSUP;
+               knote_set_error(kn, ENOTSUP);
                return 0;
        }
 
        p = proc_find(kn->kn_id);
        if (p == NULL) {
-               kn->kn_flags = EV_ERROR;
-               kn->kn_data = ESRCH;
+               knote_set_error(kn, ESRCH);
                return 0;
        }
 
@@ -815,8 +890,7 @@ filt_procattach(struct knote *kn)
                                break;  /* parent-in-waiting => ok */
 
                        proc_rele(p);
-                       kn->kn_flags = EV_ERROR;
-                       kn->kn_data = EACCES;
+                       knote_set_error(kn, EACCES);
                        return 0;
                } while (0);
 
@@ -891,7 +965,7 @@ filt_proc(struct knote *kn, long hint)
                         */
                        return 0;
                }
-       }                                       
+       }
 
        /*
         * if the user is interested in this event, record it.
@@ -909,7 +983,7 @@ filt_proc(struct knote *kn, long hint)
 
        /*
         * The kernel has a wrapper in place that returns the same data
-        * as is collected here, in kn_data.  Any changes to how 
+        * as is collected here, in kn_data.  Any changes to how
         * NOTE_EXITSTATUS and NOTE_EXIT_DETAIL are collected
         * should also be reflected in the proc_pidnoteexit() wrapper.
         */
@@ -923,7 +997,7 @@ filt_proc(struct knote *kn, long hint)
                        kn->kn_fflags |= NOTE_EXIT_DETAIL;
                        if ((kn->kn_ptr.p_proc->p_lflag &
                             P_LTERM_DECRYPTFAIL) != 0) {
-                               kn->kn_data |= NOTE_EXIT_DECRYPTFAIL; 
+                               kn->kn_data |= NOTE_EXIT_DECRYPTFAIL;
                        }
                        if ((kn->kn_ptr.p_proc->p_lflag &
                             P_LTERM_JETSAM) != 0) {
@@ -972,8 +1046,6 @@ filt_proctouch(struct knote *kn, struct kevent_internal_s *kev)
 
        /* accept new filter flags and mask off output events no long interesting */
        kn->kn_sfflags = kev->fflags;
-       if ((kn->kn_status & KN_UDATA_SPECIFIC) == 0)
-               kn->kn_udata = kev->udata;
 
        /* restrict the current results to the (smaller?) set of new interest */
        /*
@@ -1007,32 +1079,120 @@ filt_procprocess(struct knote *kn, struct filt_process_s *data, struct kevent_in
        return res;
 }
 
+SECURITY_READ_ONLY_EARLY(static struct filterops) proc_filtops = {
+       .f_attach = filt_procattach,
+       .f_detach = filt_procdetach,
+       .f_event = filt_proc,
+       .f_touch = filt_proctouch,
+       .f_process = filt_procprocess,
+};
+
+#pragma mark timer_filtops
+
+struct filt_timer_params {
+       uint64_t deadline; /* deadline in abs/cont time
+                                                 (or 0 if NOTE_ABSOLUTE and deadline is in past) */
+       uint64_t leeway;   /* leeway in abstime, or 0 if none */
+       uint64_t interval; /* interval in abstime or 0 if non-repeating timer */
+};
+
 /*
- * filt_timervalidate - process data from user
+ * Values stored in the knote at rest (using Mach absolute time units)
  *
- *     Converts to either interval or deadline format.
+ * kn->kn_hook          where the thread_call object is stored
+ * kn->kn_ext[0]        next deadline or 0 if immediate expiration
+ * kn->kn_ext[1]        leeway value
+ * kn->kn_sdata         interval timer: the interval
+ *                      absolute/deadline timer: 0
+ * kn->kn_hookid        timer state
  *
- *     The saved-data field in the knote contains the
- *     time value.  The saved filter-flags indicates
- *     the unit of measurement.
+ * TIMER_IDLE:
+ *   The timer has either never been scheduled or been cancelled.
+ *   It is safe to schedule a new one in this state.
  *
- *     After validation, either the saved-data field
- *     contains the interval in absolute time, or ext[0]
- *     contains the expected deadline. If that deadline
- *     is in the past, ext[0] is 0.
+ * TIMER_ARMED:
+ *   The timer has been scheduled
  *
- *     Returns EINVAL for unrecognized units of time.
- *
- *     Timer filter lock is held.
+ * TIMER_FIRED
+ *   The timer has fired and an event needs to be delivered.
+ *   When in this state, the callout may still be running.
  *
+ * TIMER_IMMEDIATE
+ *   The timer has fired at registration time, and the callout was never
+ *   dispatched.
  */
-static int
-filt_timervalidate(struct knote *kn)
+#define TIMER_IDLE       0x0
+#define        TIMER_ARMED      0x1
+#define TIMER_FIRED      0x2
+#define TIMER_IMMEDIATE  0x3
+
+static void
+filt_timer_set_params(struct knote *kn, struct filt_timer_params *params)
 {
-       uint64_t multiplier;
-       uint64_t raw = 0;
+       kn->kn_ext[0] = params->deadline;
+       kn->kn_ext[1] = params->leeway;
+       kn->kn_sdata  = params->interval;
+}
 
-       switch (kn->kn_sfflags & (NOTE_SECONDS|NOTE_USECONDS|NOTE_NSECONDS)) {
+/*
+ * filt_timervalidate - process data from user
+ *
+ * Sets up the deadline, interval, and leeway from the provided user data
+ *
+ * Input:
+ *      kn_sdata        timer deadline or interval time
+ *      kn_sfflags      style of timer, unit of measurement
+ *
+ * Output:
+ *      struct filter_timer_params to apply to the filter with
+ *      filt_timer_set_params when changes are ready to be commited.
+ *
+ * Returns:
+ *      EINVAL          Invalid user data parameters
+ *      ERANGE          Various overflows with the parameters
+ *
+ * Called with timer filter lock held.
+ */
+static int
+filt_timervalidate(const struct kevent_internal_s *kev,
+               struct filt_timer_params *params)
+{
+       /*
+        * There are 5 knobs that need to be chosen for a timer registration:
+        *
+        * A) Units of time (what is the time duration of the specified number)
+        *      Absolute and interval take:
+        *              NOTE_SECONDS, NOTE_USECONDS, NOTE_NSECONDS, NOTE_MACHTIME
+        *      Defaults to milliseconds if not specified
+        *
+        * B) Clock epoch (what is the zero point of the specified number)
+        *      For interval, there is none
+        *      For absolute, defaults to the gettimeofday/calendar epoch
+        *      With NOTE_MACHTIME, uses mach_absolute_time()
+        *      With NOTE_MACHTIME and NOTE_MACH_CONTINUOUS_TIME, uses mach_continuous_time()
+        *
+        * C) The knote's behavior on delivery
+        *      Interval timer causes the knote to arm for the next interval unless one-shot is set
+        *      Absolute is a forced one-shot timer which deletes on delivery
+        *      TODO: Add a way for absolute to be not forced one-shot
+        *
+        * D) Whether the time duration is relative to now or absolute
+        *      Interval fires at now + duration when it is set up
+        *      Absolute fires at now + difference between now walltime and passed in walltime
+        *      With NOTE_MACHTIME it fires at an absolute MAT or MCT.
+        *
+        * E) Whether the timer continues to tick across sleep
+        *      By default all three do not.
+        *      For interval and absolute, NOTE_MACH_CONTINUOUS_TIME causes them to tick across sleep
+        *      With NOTE_ABSOLUTE | NOTE_MACHTIME | NOTE_MACH_CONTINUOUS_TIME:
+        *              expires when mach_continuous_time() is > the passed in value.
+        */
+
+       uint64_t multiplier;
+
+       boolean_t use_abstime = FALSE;
+
+       switch (kev->fflags & (NOTE_SECONDS|NOTE_USECONDS|NOTE_NSECONDS|NOTE_MACHTIME)) {
        case NOTE_SECONDS:
                multiplier = NSEC_PER_SEC;
                break;
@@ -1042,6 +1202,10 @@ filt_timervalidate(struct knote *kn)
        case NOTE_NSECONDS:
                multiplier = 1;
                break;
+       case NOTE_MACHTIME:
+               multiplier = 0;
+               use_abstime = TRUE;
+               break;
        case 0: /* milliseconds (default) */
                multiplier = NSEC_PER_SEC / 1000;
                break;
@@ -1049,220 +1213,256 @@ filt_timervalidate(struct knote *kn)
                return (EINVAL);
        }
 
-       /* transform the slop delta(leeway) in kn_ext[1] if passed to same time scale */
-       if(kn->kn_sfflags & NOTE_LEEWAY){
-               nanoseconds_to_absolutetime((uint64_t)kn->kn_ext[1] * multiplier, &raw);
-               kn->kn_ext[1] = raw;
+       /* transform the leeway in kn_ext[1] to same time scale */
+       if (kev->fflags & NOTE_LEEWAY) {
+               uint64_t leeway_abs;
+
+               if (use_abstime) {
+                       leeway_abs = (uint64_t)kev->ext[1];
+               } else  {
+                       uint64_t leeway_ns;
+                       if (os_mul_overflow((uint64_t)kev->ext[1], multiplier, &leeway_ns))
+                               return (ERANGE);
+
+                       nanoseconds_to_absolutetime(leeway_ns, &leeway_abs);
+               }
+
+               params->leeway = leeway_abs;
+       } else {
+               params->leeway = 0;
        }
 
-       nanoseconds_to_absolutetime((uint64_t)kn->kn_sdata * multiplier, &raw);
+       if (kev->fflags & NOTE_ABSOLUTE) {
+               uint64_t deadline_abs;
+
+               if (use_abstime) {
+                       deadline_abs = (uint64_t)kev->data;
+               } else {
+                       uint64_t calendar_deadline_ns;
 
-       kn->kn_ext[0] = 0;
-       kn->kn_sdata = 0;
+                       if (os_mul_overflow((uint64_t)kev->data, multiplier, &calendar_deadline_ns))
+                               return (ERANGE);
 
-       if (kn->kn_sfflags & NOTE_ABSOLUTE) {
-               clock_sec_t seconds;
-               clock_nsec_t nanoseconds;
-               uint64_t now;
+                       /* calendar_deadline_ns is in nanoseconds since the epoch */
+
+                       clock_sec_t seconds;
+                       clock_nsec_t nanoseconds;
+
+                       /*
+                        * Note that the conversion through wall-time is only done once.
+                        *
+                        * If the relationship between MAT and gettimeofday changes,
+                        * the underlying timer does not update.
+                        *
+                        * TODO: build a wall-time denominated timer_call queue
+                        * and a flag to request DTRTing with wall-time timers
+                        */
+                       clock_get_calendar_nanotime(&seconds, &nanoseconds);
+
+                       uint64_t calendar_now_ns = (uint64_t)seconds * NSEC_PER_SEC + nanoseconds;
+
+                       /* if deadline is in the future */
+                       if (calendar_now_ns < calendar_deadline_ns) {
+                               uint64_t interval_ns = calendar_deadline_ns - calendar_now_ns;
+                               uint64_t interval_abs;
 
-               clock_get_calendar_nanotime(&seconds, &nanoseconds);
-               nanoseconds_to_absolutetime((uint64_t)seconds * NSEC_PER_SEC +
-                   nanoseconds, &now);
+                               nanoseconds_to_absolutetime(interval_ns, &interval_abs);
 
-               /* if time is in the future */
-               if (now < raw) {
-                       raw -= now;
+                               /*
+                                * Note that the NOTE_MACH_CONTINUOUS_TIME flag here only
+                                * causes the timer to keep ticking across sleep, but
+                                * it does not change the calendar timebase.
+                                */
 
-                       if (kn->kn_sfflags & NOTE_MACH_CONTINUOUS_TIME) {
-                               clock_continuoustime_interval_to_deadline(raw,
-                                   &kn->kn_ext[0]);
+                               if (kev->fflags & NOTE_MACH_CONTINUOUS_TIME)
+                                       clock_continuoustime_interval_to_deadline(interval_abs,
+                                                                                 &deadline_abs);
+                               else
+                                       clock_absolutetime_interval_to_deadline(interval_abs,
+                                                                               &deadline_abs);
                        } else {
-                               clock_absolutetime_interval_to_deadline(raw,
-                                   &kn->kn_ext[0]);
+                               deadline_abs = 0; /* cause immediate expiration */
                        }
                }
+
+               params->deadline = deadline_abs;
+               params->interval = 0; /* NOTE_ABSOLUTE is non-repeating */
+       } else if (kev->data < 0) {
+               /*
+                * Negative interval timers fire immediately, once.
+                *
+                * Ideally a negative interval would be an error, but certain clients
+                * pass negative values on accident, and expect an event back.
+                *
+                * In the old implementation the timer would repeat with no delay
+                * N times until mach_absolute_time() + (N * interval) underflowed,
+                * then it would wait ~forever by accidentally arming a timer for the far future.
+                *
+                * We now skip the power-wasting hot spin phase and go straight to the idle phase.
+                */
+
+               params->deadline = 0; /* expire immediately */
+               params->interval = 0; /* non-repeating */
        } else {
-               kn->kn_sdata = raw;
+               uint64_t interval_abs = 0;
+
+               if (use_abstime) {
+                       interval_abs = (uint64_t)kev->data;
+               } else {
+                       uint64_t interval_ns;
+                       if (os_mul_overflow((uint64_t)kev->data, multiplier, &interval_ns))
+                               return (ERANGE);
+
+                       nanoseconds_to_absolutetime(interval_ns, &interval_abs);
+               }
+
+               uint64_t deadline = 0;
+
+               if (kev->fflags & NOTE_MACH_CONTINUOUS_TIME)
+                       clock_continuoustime_interval_to_deadline(interval_abs, &deadline);
+               else
+                       clock_absolutetime_interval_to_deadline(interval_abs, &deadline);
+
+               params->deadline = deadline;
+               params->interval = interval_abs;
        }
 
        return (0);
 }
 
 /*
- * filt_timerupdate - compute the next deadline
- *
- *     Repeating timers store their interval in kn_sdata. Absolute
- *     timers have already calculated the deadline, stored in ext[0].
- *
- *     On return, the next deadline (or zero if no deadline is needed)
- *     is stored in kn_ext[0].
- *
- *     Timer filter lock is held.
+ * filt_timerexpire - the timer callout routine
  */
 static void
-filt_timerupdate(struct knote *kn, int num_fired)
+filt_timerexpire(void *knx, __unused void *spare)
 {
-       assert(num_fired > 0);
-
-       /* if there's no interval, deadline is just in kn_ext[0] */
-       if (kn->kn_sdata == 0)
-               return;
+       struct knote *kn = knx;
+       int v;
 
-       /* if timer hasn't fired before, fire in interval nsecs */
-       if (kn->kn_ext[0] == 0) {
-               assert(num_fired == 1);
-               if (kn->kn_sfflags & NOTE_MACH_CONTINUOUS_TIME) {
-                       clock_continuoustime_interval_to_deadline(kn->kn_sdata,
-                           &kn->kn_ext[0]);
-               } else {
-                       clock_absolutetime_interval_to_deadline(kn->kn_sdata,
-                           &kn->kn_ext[0]);
-               }
+       if (os_atomic_cmpxchgv(&kn->kn_hookid, TIMER_ARMED, TIMER_FIRED,
+                       &v, relaxed)) {
+               // our f_event always would say FILTER_ACTIVE,
+               // so be leaner and just do it.
+               struct kqueue *kq = knote_get_kq(kn);
+               kqlock(kq);
+               knote_activate(kn);
+               kqunlock(kq);
        } else {
                /*
-                * If timer has fired before, schedule the next pop
-                * relative to the last intended deadline.
-                *
-                * We could check for whether the deadline has expired,
-                * but the thread call layer can handle that.
-                * 
-                * Go forward an additional number of periods, in the case the
-                * timer fired multiple times while the system was asleep.
+                * From TIMER_ARMED, the only allowed transition are:
+                * - to TIMER_FIRED through the timer callout just above
+                * - to TIMER_IDLE due to filt_timercancel() which will wait for the
+                *   timer callout (and any possible invocation of filt_timerexpire) to
+                *   have finished before the state is changed again.
                 */
-               kn->kn_ext[0] += (kn->kn_sdata * num_fired);
+               assert(v == TIMER_IDLE);
        }
 }
 
-/*
- * filt_timerexpire - the timer callout routine
- *
- * Just propagate the timer event into the knote
- * filter routine (by going through the knote
- * synchronization point).  Pass a hint to
- * indicate this is a real event, not just a
- * query from above.
- */
 static void
-filt_timerexpire(void *knx, __unused void *spare)
+filt_timercancel(struct knote *kn)
 {
-       struct klist timer_list;
-       struct knote *kn = knx;
-
-       filt_timerlock();
-
-       kn->kn_hookid &= ~TIMER_RUNNING;
+       if (os_atomic_xchg(&kn->kn_hookid, TIMER_IDLE, relaxed) == TIMER_ARMED) {
+               /* cancel the thread call and wait for any filt_timerexpire in flight */
+               thread_call_cancel_wait((thread_call_t)kn->kn_hook);
+       }
+}
 
-       /* no "object" for timers, so fake a list */
-       SLIST_INIT(&timer_list);
-       SLIST_INSERT_HEAD(&timer_list, kn, kn_selnext);
-       KNOTE(&timer_list, 1);
+/*
+ * Does this deadline needs a timer armed for it, or has it expired?
+ */
+static bool
+filt_timer_is_ready(struct knote *kn)
+{
+       uint64_t now, deadline = kn->kn_ext[0];
 
-       /* if someone is waiting for timer to pop */
-       if (kn->kn_hookid & TIMER_CANCELWAIT) {
-               struct kqueue *kq = knote_get_kq(kn);
-               waitq_wakeup64_all((struct waitq *)&kq->kq_wqs,
-                                  CAST_EVENT64_T(&kn->kn_hook),
-                                  THREAD_AWAKENED,
-                                  WAITQ_ALL_PRIORITIES);
+       if (deadline == 0) {
+               return true;
        }
 
-       filt_timerunlock();
+       if (kn->kn_sfflags & NOTE_MACH_CONTINUOUS_TIME) {
+               now = mach_continuous_time();
+       } else {
+               now = mach_absolute_time();
+       }
+       return deadline <= now;
 }
 
 /*
- * Cancel a running timer (or wait for the pop).
- * Timer filter lock is held.
+ * Arm a timer
+ *
+ * It is the responsibility of the caller to make sure the timer call
+ * has completed or been cancelled properly prior to arming it.
  */
 static void
-filt_timercancel(struct knote *kn)
+filt_timerarm(struct knote *kn)
 {
-       struct kqueue *kq = knote_get_kq(kn);
-       thread_call_t callout = kn->kn_hook;
-       boolean_t cancelled;
-
-       if (kn->kn_hookid & TIMER_RUNNING) {
-               /* cancel the callout if we can */
-               cancelled = thread_call_cancel(callout);
-               if (cancelled) {
-                       kn->kn_hookid &= ~TIMER_RUNNING;
-               } else {
-                       /* we have to wait for the expire routine.  */
-                       kn->kn_hookid |= TIMER_CANCELWAIT;
-                       waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
-                                           CAST_EVENT64_T(&kn->kn_hook),
-                                           THREAD_UNINT, TIMEOUT_WAIT_FOREVER);
-                       filt_timerunlock();
-                       thread_block(THREAD_CONTINUE_NULL);
-                       filt_timerlock();
-                       assert((kn->kn_hookid & TIMER_RUNNING) == 0);
-               }
-       }
+       uint64_t deadline = kn->kn_ext[0];
+       uint64_t leeway   = kn->kn_ext[1];
+
+       int filter_flags = kn->kn_sfflags;
+       unsigned int timer_flags = 0;
+
+       assert(os_atomic_load(&kn->kn_hookid, relaxed) == TIMER_IDLE);
+
+       if (filter_flags & NOTE_CRITICAL)
+               timer_flags |= THREAD_CALL_DELAY_USER_CRITICAL;
+       else if (filter_flags & NOTE_BACKGROUND)
+               timer_flags |= THREAD_CALL_DELAY_USER_BACKGROUND;
+       else
+               timer_flags |= THREAD_CALL_DELAY_USER_NORMAL;
+
+       if (filter_flags & NOTE_LEEWAY)
+               timer_flags |= THREAD_CALL_DELAY_LEEWAY;
+
+       if (filter_flags & NOTE_MACH_CONTINUOUS_TIME)
+               timer_flags |= THREAD_CALL_CONTINUOUS;
+
+       os_atomic_store(&kn->kn_hookid, TIMER_ARMED, relaxed);
+       thread_call_enter_delayed_with_leeway((thread_call_t)kn->kn_hook, NULL,
+                       deadline, leeway, timer_flags);
 }
 
 /*
  * Allocate a thread call for the knote's lifetime, and kick off the timer.
  */
 static int
-filt_timerattach(struct knote *kn)
+filt_timerattach(struct knote *kn, struct kevent_internal_s *kev)
 {
        thread_call_t callout;
+       struct filt_timer_params params;
        int error;
-       int res;
 
-       callout = thread_call_allocate(filt_timerexpire, kn);
-       if (NULL == callout) {
-               kn->kn_flags = EV_ERROR;
-               kn->kn_data = ENOMEM;
+       if ((error = filt_timervalidate(kev, &params)) != 0) {
+               knote_set_error(kn, error);
                return 0;
        }
 
-       filt_timerlock();
-       error = filt_timervalidate(kn);
-       if (error != 0) {
-               filt_timerunlock();
-               thread_call_free(callout);
-               kn->kn_flags = EV_ERROR;
-               kn->kn_data = error;
+       callout = thread_call_allocate_with_options(filt_timerexpire,
+                       (thread_call_param_t)kn, THREAD_CALL_PRIORITY_HIGH,
+                       THREAD_CALL_OPTIONS_ONCE);
+
+       if (NULL == callout) {
+               knote_set_error(kn, ENOMEM);
                return 0;
        }
 
-       kn->kn_hook = (void*)callout;
-       kn->kn_hookid = 0;
+       filt_timer_set_params(kn, &params);
+       kn->kn_hook = callout;
+       kn->kn_flags |= EV_CLEAR;
+       os_atomic_store(&kn->kn_hookid, TIMER_IDLE, relaxed);
 
-       /* absolute=EV_ONESHOT */
+       /* NOTE_ABSOLUTE implies EV_ONESHOT */
        if (kn->kn_sfflags & NOTE_ABSOLUTE)
                kn->kn_flags |= EV_ONESHOT;
 
-       filt_timerupdate(kn, 1);
-       if (kn->kn_ext[0]) {
-               kn->kn_flags |= EV_CLEAR;
-               unsigned int timer_flags = 0;
-               if (kn->kn_sfflags & NOTE_CRITICAL)
-                       timer_flags |= THREAD_CALL_DELAY_USER_CRITICAL;
-               else if (kn->kn_sfflags & NOTE_BACKGROUND)
-                       timer_flags |= THREAD_CALL_DELAY_USER_BACKGROUND;
-               else
-                       timer_flags |= THREAD_CALL_DELAY_USER_NORMAL;
-
-               if (kn->kn_sfflags & NOTE_LEEWAY)
-                       timer_flags |= THREAD_CALL_DELAY_LEEWAY;
-               if (kn->kn_sfflags & NOTE_MACH_CONTINUOUS_TIME)
-                       timer_flags |= THREAD_CALL_CONTINUOUS;
-
-               thread_call_enter_delayed_with_leeway(callout, NULL,
-                               kn->kn_ext[0], kn->kn_ext[1], timer_flags);
-
-               kn->kn_hookid |= TIMER_RUNNING;
+       if (filt_timer_is_ready(kn)) {
+               os_atomic_store(&kn->kn_hookid, TIMER_IMMEDIATE, relaxed);
+               return FILTER_ACTIVE;
        } else {
-               /* fake immediate */
-               kn->kn_data = 1;
+               filt_timerarm(kn);
+               return 0;
        }
-
-       res = (kn->kn_data > 0);
-
-       filt_timerunlock();
-
-       return res;
 }
 
 /*
@@ -1271,102 +1471,17 @@ filt_timerattach(struct knote *kn)
 static void
 filt_timerdetach(struct knote *kn)
 {
-       thread_call_t callout;
-
-       filt_timerlock();
-
-       callout = (thread_call_t)kn->kn_hook;
-       filt_timercancel(kn);
-
-       filt_timerunlock();
-
-       thread_call_free(callout);
-}
-
-
-static int filt_timer_num_fired(struct knote *kn)
-{
-       /* by default we fire a timer once */
-       int num_fired = 1;
+       __assert_only boolean_t freed;
 
        /*
-        * When the time base is mach_continuous_time, we have to calculate
-        * the number of times the timer fired while we were asleep.
+        * Unconditionally cancel to make sure there can't be any filt_timerexpire()
+        * running anymore.
         */
-       if ((kn->kn_sfflags & NOTE_MACH_CONTINUOUS_TIME) &&
-           (kn->kn_sdata  != 0) &&
-           (kn->kn_ext[0] != 0))
-       {
-               const uint64_t now = mach_continuous_time();
-               // time for timer to fire (right now) is kn_ext[0]
-               // kn_sdata is period for timer to fire
-               assert(now >= kn->kn_ext[0]);
-               assert(kn->kn_sdata > 0);
-
-               const uint64_t overrun_ticks = now - kn->kn_ext[0];
-               const uint64_t kn_sdata = kn->kn_sdata;
-
-               if (overrun_ticks < kn_sdata) {
-                       num_fired = 1;
-               } else if (overrun_ticks < (kn_sdata << 1)) {
-                       num_fired = 2;
-               } else {
-                       num_fired = (overrun_ticks / kn_sdata) + 1;
-               }
-       }
-
-       return num_fired;
-}
-
-/*
- * filt_timer - post events to a timer knote
- *
- * Count the timer fire and re-arm as requested.
- * This always crosses the threshold of interest,
- * so always return an indication that the knote
- * should be activated (if not already).
- */
-static int
-filt_timer(
-       struct knote *kn, 
-       long hint)
-{
-#pragma unused(hint)
-
-       /* real timer pop -- timer lock held by filt_timerexpire */
-       int num_fired = filt_timer_num_fired(kn);
-       kn->kn_data += num_fired;
-
-       if (((kn->kn_hookid & TIMER_CANCELWAIT) == 0) &&
-           ((kn->kn_flags & EV_ONESHOT) == 0)) {
-               /* evaluate next time to fire */
-               filt_timerupdate(kn, num_fired);
-
-               if (kn->kn_ext[0]) {
-                       unsigned int timer_flags = 0;
-
-                       /* keep the callout and re-arm */
-                       if (kn->kn_sfflags & NOTE_CRITICAL)
-                               timer_flags |= THREAD_CALL_DELAY_USER_CRITICAL;
-                       else if (kn->kn_sfflags & NOTE_BACKGROUND)
-                               timer_flags |= THREAD_CALL_DELAY_USER_BACKGROUND;
-                       else
-                               timer_flags |= THREAD_CALL_DELAY_USER_NORMAL;
-
-                       if (kn->kn_sfflags & NOTE_LEEWAY)
-                               timer_flags |= THREAD_CALL_DELAY_LEEWAY;
-
-                       thread_call_enter_delayed_with_leeway(kn->kn_hook, NULL,
-                                       kn->kn_ext[0], kn->kn_ext[1], timer_flags);
-
-                       kn->kn_hookid |= TIMER_RUNNING;
-               }
-       }
-       return (1);
+       thread_call_cancel_wait((thread_call_t)kn->kn_hook);
+       freed = thread_call_free((thread_call_t)kn->kn_hook);
+       assert(freed);
 }
 
-
-
 /*
  * filt_timertouch - update timer knote with new user input
  *
@@ -1375,67 +1490,36 @@ filt_timer(
  * pops have gone off (in kn_data).
  */
 static int
-filt_timertouch(
-       struct knote *kn,
-       struct kevent_internal_s *kev)
+filt_timertouch(struct knote *kn, struct kevent_internal_s *kev)
 {
+       struct filt_timer_params params;
+       uint32_t changed_flags = (kn->kn_sfflags ^ kev->fflags);
        int error;
-       int res;
 
-       filt_timerlock();
+       if (changed_flags & NOTE_ABSOLUTE) {
+               kev->flags |= EV_ERROR;
+               kev->data = EINVAL;
+               return 0;
+       }
 
-       /* cancel current call */
-       filt_timercancel(kn);
+       if ((error = filt_timervalidate(kev, &params)) != 0) {
+               kev->flags |= EV_ERROR;
+               kev->data = error;
+               return 0;
+       }
 
        /* capture the new values used to compute deadline */
-       kn->kn_sdata = kev->data;
+       filt_timercancel(kn);
+       filt_timer_set_params(kn, &params);
        kn->kn_sfflags = kev->fflags;
-       kn->kn_ext[0] = kev->ext[0];
-       kn->kn_ext[1] = kev->ext[1];
-
-       if ((kn->kn_status & KN_UDATA_SPECIFIC) == 0)
-               kn->kn_udata = kev->udata;
-
-       /* recalculate deadline */
-       error = filt_timervalidate(kn);
-       if (error) {
-               /* no way to report error, so mark it in the knote */
-               filt_timerunlock();
-               kn->kn_flags |= EV_ERROR;
-               kn->kn_data = error;
-               return 1;
-       }
 
-       /* start timer if necessary */
-       filt_timerupdate(kn, 1);
-
-       if (kn->kn_ext[0]) {
-               unsigned int timer_flags = 0;
-               if (kn->kn_sfflags & NOTE_CRITICAL)
-                       timer_flags |= THREAD_CALL_DELAY_USER_CRITICAL;
-               else if (kn->kn_sfflags & NOTE_BACKGROUND)
-                       timer_flags |= THREAD_CALL_DELAY_USER_BACKGROUND;
-               else
-                       timer_flags |= THREAD_CALL_DELAY_USER_NORMAL;
-
-               if (kn->kn_sfflags & NOTE_LEEWAY)
-                       timer_flags |= THREAD_CALL_DELAY_LEEWAY;
-
-               thread_call_enter_delayed_with_leeway(kn->kn_hook, NULL,
-                               kn->kn_ext[0], kn->kn_ext[1], timer_flags);
-
-               kn->kn_hookid |= TIMER_RUNNING;
+       if (filt_timer_is_ready(kn)) {
+               os_atomic_store(&kn->kn_hookid, TIMER_IMMEDIATE, relaxed);
+               return FILTER_ACTIVE | FILTER_UPDATE_REQ_QOS;
        } else {
-               /* pretend the timer has fired */
-               kn->kn_data = 1;
+               filt_timerarm(kn);
+               return FILTER_UPDATE_REQ_QOS;
        }
-
-       /* capture if already fired */
-       res = (kn->kn_data > 0);
-
-       filt_timerunlock();
-
-       return res;
 }
 
 /*
@@ -1451,66 +1535,117 @@ filt_timerprocess(
        __unused struct filt_process_s *data,
        struct kevent_internal_s *kev)
 {
-       filt_timerlock();
-
-       /* user-query */
-       if (kn->kn_data == 0) {
-               filt_timerunlock();
+       /*
+        * filt_timerprocess is serialized with any filter routine except for
+        * filt_timerexpire which atomically does a TIMER_ARMED -> TIMER_FIRED
+        * transition, and on success, activates the knote.
+        *
+        * Hence, we don't need atomic modifications of the state, only to peek at
+        * whether we see any of the "FIRED" state, and if we do, it is safe to
+        * do simple state machine transitions.
+        */
+       switch (os_atomic_load(&kn->kn_hookid, relaxed)) {
+       case TIMER_IDLE:
+       case TIMER_ARMED:
+               /*
+                * This can happen if a touch resets a timer that had fired
+                * without being processed
+                */
                return 0;
        }
 
+       os_atomic_store(&kn->kn_hookid, TIMER_IDLE, relaxed);
+
        /*
         * Copy out the interesting kevent state,
         * but don't leak out the raw time calculations.
+        *
+        * TODO: potential enhancements - tell the user about:
+        *      - deadline to which this timer thought it was expiring
+        *      - return kn_sfflags in the fflags field so the client can know
+        *        under what flags the timer fired
         */
        *kev = kn->kn_kevent;
        kev->ext[0] = 0;
        /* kev->ext[1] = 0;  JMM - shouldn't we hide this too? */
 
-       /*
-        * reset the timer pop count in kn_data
-        * and (optionally) clear the fflags.
-        */
-       kn->kn_data = 0;
-       if (kn->kn_flags & EV_CLEAR)
-               kn->kn_fflags = 0;
+       if (kn->kn_sdata == 0) {
+               kev->data = 1;
+       } else {
+               /*
+                * This is a 'repeating' timer, so we have to emit
+                * how many intervals expired between the arm
+                * and the process.
+                *
+                * A very strange style of interface, because
+                * this could easily be done in the client...
+                */
 
-       filt_timerunlock();
-       return 1;
-}
+               uint64_t now;
 
-static void
-filt_timerlock(void)
-{
-       lck_mtx_lock(&_filt_timerlock);
-}
+               if (kn->kn_sfflags & NOTE_MACH_CONTINUOUS_TIME)
+                       now = mach_continuous_time();
+               else
+                       now = mach_absolute_time();
 
-static void
-filt_timerunlock(void)
-{
-       lck_mtx_unlock(&_filt_timerlock);
-}
+               uint64_t first_deadline = kn->kn_ext[0];
+               uint64_t interval_abs   = kn->kn_sdata;
+               uint64_t orig_arm_time  = first_deadline - interval_abs;
 
-static void
-filt_userlock(void)
-{
-       lck_spin_lock(&_filt_userlock);
-}
+               assert(now > orig_arm_time);
+               assert(now > first_deadline);
 
-static void
-filt_userunlock(void)
-{
-       lck_spin_unlock(&_filt_userlock);
+               uint64_t elapsed = now - orig_arm_time;
+
+               uint64_t num_fired = elapsed / interval_abs;
+
+               /*
+                * To reach this code, we must have seen the timer pop
+                * and be in repeating mode, so therefore it must have been
+                * more than 'interval' time since the attach or last
+                * successful touch.
+                */
+               assert(num_fired > 0);
+
+               /* report how many intervals have elapsed to the user */
+               kev->data = (int64_t)num_fired;
+
+               /* We only need to re-arm the timer if it's not about to be destroyed */
+               if ((kn->kn_flags & EV_ONESHOT) == 0) {
+                       /* fire at the end of the next interval */
+                       uint64_t new_deadline = first_deadline + num_fired * interval_abs;
+
+                       assert(new_deadline > now);
+
+                       kn->kn_ext[0] = new_deadline;
+
+                       /*
+                        * This can't shortcut setting up the thread call, because
+                        * knote_process deactivates EV_CLEAR knotes unconditionnally.
+                        */
+                       filt_timerarm(kn);
+               }
+       }
+
+       return FILTER_ACTIVE;
 }
 
+SECURITY_READ_ONLY_EARLY(static struct filterops) timer_filtops = {
+       .f_extended_codes = true,
+       .f_attach   = filt_timerattach,
+       .f_detach   = filt_timerdetach,
+       .f_event    = filt_badevent,
+       .f_touch    = filt_timertouch,
+       .f_process  = filt_timerprocess,
+};
+
+#pragma mark user_filtops
+
 static int
-filt_userattach(struct knote *kn)
+filt_userattach(struct knote *kn, __unused struct kevent_internal_s *kev)
 {
-       /* EVFILT_USER knotes are not attached to anything in the kernel */
-       /* Cant discover this knote until after attach - so no lock needed */
-       kn->kn_hook = NULL;
-       if (kn->kn_fflags & NOTE_TRIGGER) {
-               kn->kn_hookid = 1;
+       if (kn->kn_sfflags & NOTE_TRIGGER) {
+               kn->kn_hookid = FILTER_ACTIVE;
        } else {
                kn->kn_hookid = 0;
        }
@@ -1524,24 +1659,10 @@ filt_userdetach(__unused struct knote *kn)
 }
 
 static int
-filt_user(
-       __unused struct knote *kn,
-       __unused long hint)
-{
-       panic("filt_user");
-       return 0;
-}
-
-static int
-filt_usertouch(
-       struct knote *kn,
-       struct kevent_internal_s *kev)
+filt_usertouch(struct knote *kn, struct kevent_internal_s *kev)
 {
        uint32_t ffctrl;
        int fflags;
-       int active;
-
-       filt_userlock();
 
        ffctrl = kev->fflags & NOTE_FFCTRLMASK;
        fflags = kev->fflags & NOTE_FFLAGSMASK;
@@ -1560,17 +1681,10 @@ filt_usertouch(
        }
        kn->kn_sdata = kev->data;
 
-       if ((kn->kn_status & KN_UDATA_SPECIFIC) == 0)
-               kn->kn_udata = kev->udata;
-
        if (kev->fflags & NOTE_TRIGGER) {
-               kn->kn_hookid = 1;
+               kn->kn_hookid = FILTER_ACTIVE;
        }
-       active = kn->kn_hookid;
-
-       filt_userunlock();
-
-       return (active);
+       return (int)kn->kn_hookid;
 }
 
 static int
@@ -1579,34 +1693,818 @@ filt_userprocess(
        __unused struct filt_process_s *data,
        struct kevent_internal_s *kev)
 {
-       filt_userlock();
+       int result = (int)kn->kn_hookid;
 
-       if (kn->kn_hookid == 0) {
-               filt_userunlock();
-               return 0;
+       if (result) {
+               *kev = kn->kn_kevent;
+               kev->fflags = kn->kn_sfflags;
+               kev->data = kn->kn_sdata;
+               if (kn->kn_flags & EV_CLEAR) {
+                       kn->kn_hookid = 0;
+                       kn->kn_data = 0;
+                       kn->kn_fflags = 0;
+               }
        }
 
-       *kev = kn->kn_kevent;
-       kev->fflags = (volatile UInt32)kn->kn_sfflags;
-       kev->data = kn->kn_sdata;
-       if (kn->kn_flags & EV_CLEAR) {
-               kn->kn_hookid = 0;
-               kn->kn_data = 0;
-               kn->kn_fflags = 0;
-       }
-       filt_userunlock();
+       return result;
+}
+
+SECURITY_READ_ONLY_EARLY(static struct filterops) user_filtops = {
+       .f_extended_codes = true,
+       .f_attach  = filt_userattach,
+       .f_detach  = filt_userdetach,
+       .f_event   = filt_badevent,
+       .f_touch   = filt_usertouch,
+       .f_process = filt_userprocess,
+};
+
+#pragma mark workloop_filtops
 
-       return 1;
+static inline void
+filt_wllock(struct kqworkloop *kqwl)
+{
+       lck_mtx_lock(&kqwl->kqwl_statelock);
 }
 
+static inline void
+filt_wlunlock(struct kqworkloop *kqwl)
+{
+       lck_mtx_unlock(&kqwl->kqwl_statelock);
+}
+
+/*
+ * Returns true when the interlock for the turnstile is the workqueue lock
+ *
+ * When this is the case, all turnstiles operations are delegated
+ * to the workqueue subsystem.
+ *
+ * This is required because kqueue_threadreq_bind_prepost only holds the
+ * workqueue lock but needs to move the inheritor from the workloop turnstile
+ * away from the creator thread, so that this now fulfilled request cannot be
+ * picked anymore by other threads.
+ */
+static inline bool
+filt_wlturnstile_interlock_is_workq(struct kqworkloop *kqwl)
+{
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       return (kqr->kqr_state & KQR_THREQUESTED) &&
+                       (kqr->kqr_thread == THREAD_NULL);
+}
+
+static void
+filt_wlupdate_inheritor(struct kqworkloop *kqwl, struct turnstile *ts,
+               turnstile_update_flags_t flags)
+{
+       turnstile_inheritor_t inheritor = TURNSTILE_INHERITOR_NULL;
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+
+       /*
+        * binding to the workq should always happen through
+        * workq_kern_threadreq_update_inheritor()
+        */
+       assert(!filt_wlturnstile_interlock_is_workq(kqwl));
+
+       if ((inheritor = kqwl->kqwl_owner)) {
+               flags |= TURNSTILE_INHERITOR_THREAD;
+       } else if ((inheritor = kqr->kqr_thread)) {
+               flags |= TURNSTILE_INHERITOR_THREAD;
+       }
+
+       turnstile_update_inheritor(ts, inheritor, flags);
+}
+
+#define FILT_WLATTACH 0
+#define FILT_WLTOUCH  1
+#define FILT_WLDROP   2
+
+__result_use_check
+static int
+filt_wlupdate(struct kqworkloop *kqwl, struct knote *kn,
+               struct kevent_internal_s *kev, kq_index_t qos_index, int op)
+{
+       user_addr_t uaddr = CAST_USER_ADDR_T(kev->ext[EV_EXTIDX_WL_ADDR]);
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       thread_t cur_owner, new_owner, extra_thread_ref = THREAD_NULL;
+       kq_index_t cur_owner_override = THREAD_QOS_UNSPECIFIED;
+       int action = KQWL_UTQ_NONE, error = 0;
+       bool needs_wake = false, needs_wllock = false;
+       uint64_t kdata = kev->ext[EV_EXTIDX_WL_VALUE];
+       uint64_t mask = kev->ext[EV_EXTIDX_WL_MASK];
+       uint64_t udata = 0;
+
+       if (kev->fflags & (NOTE_WL_END_OWNERSHIP | NOTE_WL_DISCOVER_OWNER)) {
+               /*
+                * If we're maybe going to change the kqwl_owner,
+                * then we need to hold the filt_wllock().
+                */
+               needs_wllock = true;
+       } else if (kqr->kqr_thread == current_thread()) {
+               /*
+                * <rdar://problem/41531764> Servicer updates need to be serialized with
+                * any ownership change too, as the kqr_thread value influences the
+                * outcome of handling NOTE_WL_DISCOVER_OWNER.
+                */
+               needs_wllock = true;
+       }
+
+       if (needs_wllock) {
+               filt_wllock(kqwl);
+               /*
+                * The kqwl owner is set under both the req and filter lock,
+                * meaning it's fine to look at it under any.
+                */
+               new_owner = cur_owner = kqwl->kqwl_owner;
+       } else {
+               new_owner = cur_owner = THREAD_NULL;
+       }
+
+       /*
+        * Phase 1:
+        *
+        * If asked, load the uint64 value at the user provided address and compare
+        * it against the passed in mask and expected value.
+        *
+        * If NOTE_WL_DISCOVER_OWNER is specified, translate the loaded name as
+        * a thread reference.
+        *
+        * If NOTE_WL_END_OWNERSHIP is specified and the currently known owner is
+        * the current thread, then end ownership.
+        *
+        * Lastly decide whether we need to perform a QoS update.
+        */
+       if (uaddr) {
+               error = copyin_word(uaddr, &udata, sizeof(udata));
+               if (error) {
+                       goto out;
+               }
+
+               /* Update state as copied in.  */
+               kev->ext[EV_EXTIDX_WL_VALUE] = udata;
+
+               if ((udata & mask) != (kdata & mask)) {
+                       error = ESTALE;
+               } else if (kev->fflags & NOTE_WL_DISCOVER_OWNER) {
+                       /*
+                        * Decipher the owner port name, and translate accordingly.
+                        * The low 2 bits were borrowed for other flags, so mask them off.
+                        *
+                        * Then attempt translation to a thread reference or fail.
+                        */
+                       mach_port_name_t name = (mach_port_name_t)udata & ~0x3;
+                       if (name != MACH_PORT_NULL) {
+                               name = ipc_entry_name_mask(name);
+                               extra_thread_ref = port_name_to_thread(name);
+                               if (extra_thread_ref == THREAD_NULL) {
+                                       error = EOWNERDEAD;
+                                       goto out;
+                               }
+                               new_owner = extra_thread_ref;
+                       }
+               }
+       }
+
+       if ((kev->fflags & NOTE_WL_END_OWNERSHIP) && new_owner == current_thread()) {
+               new_owner = THREAD_NULL;
+       }
+
+       if (error == 0) {
+               if ((kev->fflags & NOTE_WL_THREAD_REQUEST) && (kev->flags & EV_DELETE)) {
+                       action = KQWL_UTQ_SET_QOS_INDEX;
+               } else if (qos_index && kqr->kqr_qos_index != qos_index) {
+                       action = KQWL_UTQ_SET_QOS_INDEX;
+               }
+
+               if (op == FILT_WLTOUCH) {
+                       /*
+                        * Save off any additional fflags/data we just accepted
+                        * But only keep the last round of "update" bits we acted on which helps
+                        * debugging a lot.
+                        */
+                       kn->kn_sfflags &= ~NOTE_WL_UPDATES_MASK;
+                       kn->kn_sfflags |= kev->fflags;
+                       kn->kn_sdata = kev->data;
+                       if (kev->fflags & NOTE_WL_SYNC_WAKE) {
+                               needs_wake = (kn->kn_hook != THREAD_NULL);
+                       }
+               } else if (op == FILT_WLDROP) {
+                       if ((kn->kn_sfflags & (NOTE_WL_SYNC_WAIT | NOTE_WL_SYNC_WAKE)) ==
+                                       NOTE_WL_SYNC_WAIT) {
+                               /*
+                                * When deleting a SYNC_WAIT knote that hasn't been woken up
+                                * explicitly, issue a wake up.
+                                */
+                               kn->kn_sfflags |= NOTE_WL_SYNC_WAKE;
+                               needs_wake = (kn->kn_hook != THREAD_NULL);
+                       }
+               }
+       }
+
+       /*
+        * Phase 2:
+        *
+        * Commit ownership and QoS changes if any, possibly wake up waiters
+        */
+
+       if (cur_owner == new_owner && action == KQWL_UTQ_NONE && !needs_wake) {
+               goto out;
+       }
+
+       kq_req_lock(kqwl);
+
+       /* If already tracked as servicer, don't track as owner */
+       if (new_owner == kqr->kqr_thread) {
+               new_owner = THREAD_NULL;
+       }
+
+       if (cur_owner != new_owner) {
+               kqwl->kqwl_owner = new_owner;
+               if (new_owner == extra_thread_ref) {
+                       /* we just transfered this ref to kqwl_owner */
+                       extra_thread_ref = THREAD_NULL;
+               }
+               cur_owner_override = kqworkloop_owner_override(kqwl);
+
+               if (cur_owner) {
+                       thread_ends_owning_workloop(cur_owner);
+               }
+
+               if (new_owner) {
+                       /* override it before we drop the old */
+                       if (cur_owner_override != THREAD_QOS_UNSPECIFIED) {
+                               thread_add_ipc_override(new_owner, cur_owner_override);
+                       }
+                       thread_starts_owning_workloop(new_owner);
+                       if ((kqr->kqr_state & KQR_THREQUESTED) && !kqr->kqr_thread) {
+                               if (action == KQWL_UTQ_NONE) {
+                                       action = KQWL_UTQ_REDRIVE_EVENTS;
+                               }
+                       }
+               } else {
+                       if ((kqr->kqr_state & (KQR_THREQUESTED | KQR_WAKEUP)) == KQR_WAKEUP) {
+                               if (action == KQWL_UTQ_NONE) {
+                                       action = KQWL_UTQ_REDRIVE_EVENTS;
+                               }
+                       }
+               }
+       }
+
+       struct turnstile *ts = kqwl->kqwl_turnstile;
+       bool wl_inheritor_updated = false;
+
+       if (action != KQWL_UTQ_NONE) {
+               kqworkloop_update_threads_qos(kqwl, action, qos_index);
+       }
+
+       if (cur_owner != new_owner && ts) {
+               if (action == KQWL_UTQ_REDRIVE_EVENTS) {
+                       /*
+                        * Note that when action is KQWL_UTQ_REDRIVE_EVENTS,
+                        * the code went through workq_kern_threadreq_initiate()
+                        * and the workqueue has set the inheritor already
+                        */
+                       assert(filt_wlturnstile_interlock_is_workq(kqwl));
+               } else if (filt_wlturnstile_interlock_is_workq(kqwl)) {
+                       workq_kern_threadreq_lock(kqwl->kqwl_p);
+                       workq_kern_threadreq_update_inheritor(kqwl->kqwl_p, kqr, new_owner,
+                                       ts, TURNSTILE_IMMEDIATE_UPDATE);
+                       workq_kern_threadreq_unlock(kqwl->kqwl_p);
+                       if (!filt_wlturnstile_interlock_is_workq(kqwl)) {
+                               /*
+                                * If the workq is no longer the interlock, then
+                                * workq_kern_threadreq_update_inheritor() has finished a bind
+                                * and we need to fallback to the regular path.
+                                */
+                               filt_wlupdate_inheritor(kqwl, ts, TURNSTILE_IMMEDIATE_UPDATE);
+                       }
+                       wl_inheritor_updated = true;
+               } else {
+                       filt_wlupdate_inheritor(kqwl, ts, TURNSTILE_IMMEDIATE_UPDATE);
+                       wl_inheritor_updated = true;
+               }
+
+               /*
+                * We need a turnstile reference because we are dropping the interlock
+                * and the caller has not called turnstile_prepare.
+                */
+               if (wl_inheritor_updated) {
+                       turnstile_reference(ts);
+               }
+       }
+
+       if (needs_wake && ts) {
+               waitq_wakeup64_thread(&ts->ts_waitq, CAST_EVENT64_T((event_t)kn),
+                               (thread_t)kn->kn_hook, THREAD_AWAKENED);
+       }
+
+       kq_req_unlock(kqwl);
+
+       if (wl_inheritor_updated) {
+               turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_NOT_HELD);
+               turnstile_deallocate(ts);
+       }
+
+out:
+       /*
+        * Phase 3:
+        *
+        * Unlock and cleanup various lingering references and things.
+        */
+       if (needs_wllock) {
+               filt_wlunlock(kqwl);
+       }
+
+#if CONFIG_WORKLOOP_DEBUG
+       KQWL_HISTORY_WRITE_ENTRY(kqwl, {
+               .updater = current_thread(),
+               .servicer = kqr->kqr_thread, /* Note: racy */
+               .old_owner = cur_owner,
+               .new_owner = new_owner,
+
+               .kev_ident  = kev->ident,
+               .error      = (int16_t)error,
+               .kev_flags  = kev->flags,
+               .kev_fflags = kev->fflags,
+
+               .kev_mask   = mask,
+               .kev_value  = kdata,
+               .in_value   = udata,
+       });
+#endif // CONFIG_WORKLOOP_DEBUG
+
+       if (cur_owner && new_owner != cur_owner) {
+               if (cur_owner_override != THREAD_QOS_UNSPECIFIED) {
+                       thread_drop_ipc_override(cur_owner);
+               }
+               thread_deallocate(cur_owner);
+       }
+
+       if (extra_thread_ref) {
+               thread_deallocate(extra_thread_ref);
+       }
+       return error;
+}
+
+/*
+ * Remembers the last updated that came in from userspace for debugging reasons.
+ * - fflags is mirrored from the userspace kevent
+ * - ext[i, i != VALUE] is mirrored from the userspace kevent
+ * - ext[VALUE] is set to what the kernel loaded atomically
+ * - data is set to the error if any
+ */
+static inline void
+filt_wlremember_last_update(struct knote *kn, struct kevent_internal_s *kev,
+               int error)
+{
+       kn->kn_fflags = kev->fflags;
+       kn->kn_data = error;
+       memcpy(kn->kn_ext, kev->ext, sizeof(kev->ext));
+}
+
+static int
+filt_wlattach(struct knote *kn, struct kevent_internal_s *kev)
+{
+       struct kqueue *kq = knote_get_kq(kn);
+       struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+       int error = 0;
+       kq_index_t qos_index = 0;
+
+       if ((kq->kq_state & KQ_WORKLOOP) == 0) {
+               error = ENOTSUP;
+               goto out;
+       }
+
+#if DEVELOPMENT || DEBUG
+       if (kev->ident == 0 && kev->udata == 0 && kev->fflags == 0) {
+               struct kqrequest *kqr = &kqwl->kqwl_request;
+
+               kq_req_lock(kqwl);
+               kev->fflags = 0;
+               if (kqr->kqr_dsync_waiters) {
+                       kev->fflags |= NOTE_WL_SYNC_WAIT;
+               }
+               if (kqr->kqr_qos_index) {
+                       kev->fflags |= NOTE_WL_THREAD_REQUEST;
+               }
+               kev->ext[0] = thread_tid(kqwl->kqwl_owner);
+               kev->ext[1] = thread_tid(kqwl->kqwl_request.kqr_thread);
+               kev->ext[2] = thread_owned_workloops_count(current_thread());
+               kev->ext[3] = kn->kn_kevent.ext[3];
+               kq_req_unlock(kqwl);
+               error = EBUSY;
+               goto out;
+       }
+#endif
+
+       int command = (kn->kn_sfflags & NOTE_WL_COMMANDS_MASK);
+       switch (command) {
+       case NOTE_WL_THREAD_REQUEST:
+               if (kn->kn_id != kqwl->kqwl_dynamicid) {
+                       error = EINVAL;
+                       goto out;
+               }
+               qos_index = _pthread_priority_thread_qos(kn->kn_qos);
+               if (qos_index == THREAD_QOS_UNSPECIFIED) {
+                       error = ERANGE;
+                       goto out;
+               }
+               if (kqwl->kqwl_request.kqr_qos_index) {
+                       /*
+                        * There already is a thread request, and well, you're only allowed
+                        * one per workloop, so fail the attach.
+                        */
+                       error = EALREADY;
+                       goto out;
+               }
+               break;
+       case NOTE_WL_SYNC_WAIT:
+       case NOTE_WL_SYNC_WAKE:
+               if (kn->kn_id == kqwl->kqwl_dynamicid) {
+                       error = EINVAL;
+                       goto out;
+               }
+               if ((kn->kn_flags & EV_DISABLE) == 0) {
+                       error = EINVAL;
+                       goto out;
+               }
+               if (kn->kn_sfflags & NOTE_WL_END_OWNERSHIP) {
+                       error = EINVAL;
+                       goto out;
+               }
+               break;
+       default:
+               error = EINVAL;
+               goto out;
+       }
+
+       error = filt_wlupdate(kqwl, kn, kev, qos_index, FILT_WLATTACH);
+
+out:
+       if (error) {
+               /* If userland wants ESTALE to be hidden, fail the attach anyway */
+               if (error == ESTALE && (kn->kn_sfflags & NOTE_WL_IGNORE_ESTALE)) {
+                       error = 0;
+               }
+               knote_set_error(kn, error);
+               return 0;
+       }
+       if (command == NOTE_WL_SYNC_WAIT) {
+               return kevent_register_wait_prepare(kn, kev);
+       }
+       /* Just attaching the thread request successfully will fire it */
+       if (command == NOTE_WL_THREAD_REQUEST) {
+               /*
+                * Thread Request knotes need an explicit touch to be active again,
+                * so delivering an event needs to also consume it.
+                */
+               kn->kn_flags |= EV_CLEAR;
+               return FILTER_ACTIVE;
+       }
+       return 0;
+}
+
+static void __dead2
+filt_wlwait_continue(void *parameter, wait_result_t wr)
+{
+       struct _kevent_register *cont_args = parameter;
+       struct kqworkloop *kqwl = (struct kqworkloop *)cont_args->kq;
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+
+       kq_req_lock(kqwl);
+       kqr->kqr_dsync_waiters--;
+       if (filt_wlturnstile_interlock_is_workq(kqwl)) {
+               workq_kern_threadreq_lock(kqwl->kqwl_p);
+               turnstile_complete((uintptr_t)kqwl, &kqwl->kqwl_turnstile, NULL);
+               workq_kern_threadreq_unlock(kqwl->kqwl_p);
+       } else {
+               turnstile_complete((uintptr_t)kqwl, &kqwl->kqwl_turnstile, NULL);
+       }
+       kq_req_unlock(kqwl);
+
+       turnstile_cleanup();
+
+       if (wr == THREAD_INTERRUPTED) {
+               cont_args->kev.flags |= EV_ERROR;
+               cont_args->kev.data = EINTR;
+       } else if (wr != THREAD_AWAKENED) {
+               panic("Unexpected wait result: %d", wr);
+       }
+
+       kevent_register_wait_return(cont_args);
+}
+
+/*
+ * Called with the workloop mutex held, most of the time never returns as it
+ * calls filt_wlwait_continue through a continuation.
+ */
+static void __dead2
+filt_wlpost_register_wait(struct uthread *uth, struct knote_lock_ctx *knlc,
+               struct _kevent_register *cont_args)
+{
+       struct kqworkloop *kqwl = (struct kqworkloop *)cont_args->kq;
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       struct turnstile *ts;
+       bool workq_locked = false;
+
+       kq_req_lock(kqwl);
+
+       kqr->kqr_dsync_waiters++;
+
+       if (filt_wlturnstile_interlock_is_workq(kqwl)) {
+               workq_kern_threadreq_lock(kqwl->kqwl_p);
+               workq_locked = true;
+       }
+
+       ts = turnstile_prepare((uintptr_t)kqwl, &kqwl->kqwl_turnstile,
+                       TURNSTILE_NULL, TURNSTILE_WORKLOOPS);
+
+       if (workq_locked) {
+               workq_kern_threadreq_update_inheritor(kqwl->kqwl_p,
+                               &kqwl->kqwl_request, kqwl->kqwl_owner, ts,
+                               TURNSTILE_DELAYED_UPDATE);
+               if (!filt_wlturnstile_interlock_is_workq(kqwl)) {
+                       /*
+                        * if the interlock is no longer the workqueue lock,
+                        * then we don't need to hold it anymore.
+                        */
+                       workq_kern_threadreq_unlock(kqwl->kqwl_p);
+                       workq_locked = false;
+               }
+       }
+       if (!workq_locked) {
+               /*
+                * If the interlock is the workloop's, then it's our responsibility to
+                * call update_inheritor, so just do it.
+                */
+               filt_wlupdate_inheritor(kqwl, ts, TURNSTILE_DELAYED_UPDATE);
+       }
+
+       thread_set_pending_block_hint(uth->uu_thread, kThreadWaitWorkloopSyncWait);
+       waitq_assert_wait64(&ts->ts_waitq, CAST_EVENT64_T(cont_args->knote),
+                       THREAD_ABORTSAFE, TIMEOUT_WAIT_FOREVER);
+
+       if (workq_locked) {
+               workq_kern_threadreq_unlock(kqwl->kqwl_p);
+       }
+
+       thread_t thread = kqwl->kqwl_owner ?: kqr->kqr_thread;
+       if (thread) {
+               thread_reference(thread);
+       }
+       kq_req_unlock(kqwl);
+
+       kevent_register_wait_block(ts, thread, knlc, filt_wlwait_continue, cont_args);
+}
+
+/* called in stackshot context to report the thread responsible for blocking this thread */
+void
+kdp_workloop_sync_wait_find_owner(__assert_only thread_t thread,
+               event64_t event, thread_waitinfo_t *waitinfo)
+{
+       struct knote *kn = (struct knote *)event;
+       assert(kdp_is_in_zone(kn, "knote zone"));
+
+       assert(kn->kn_hook == thread);
+
+       struct kqueue *kq = knote_get_kq(kn);
+       assert(kdp_is_in_zone(kq, "kqueue workloop zone"));
+       assert(kq->kq_state & KQ_WORKLOOP);
+
+       struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+
+       thread_t kqwl_owner = kqwl->kqwl_owner;
+       thread_t servicer = kqr->kqr_thread;
+
+       if (kqwl_owner != THREAD_NULL) {
+               assert(kdp_is_in_zone(kqwl_owner, "threads"));
+
+               waitinfo->owner = thread_tid(kqwl->kqwl_owner);
+       } else if (servicer != THREAD_NULL) {
+               assert(kdp_is_in_zone(servicer, "threads"));
+
+               waitinfo->owner = thread_tid(servicer);
+       } else if (kqr->kqr_state & KQR_THREQUESTED) {
+               waitinfo->owner = STACKSHOT_WAITOWNER_THREQUESTED;
+       } else {
+               waitinfo->owner = 0;
+       }
+
+       waitinfo->context = kqwl->kqwl_dynamicid;
+}
+
+static void
+filt_wldetach(__assert_only struct knote *kn)
+{
+       assert(knote_get_kq(kn)->kq_state & KQ_WORKLOOP);
+       if (kn->kn_hook) {
+               kevent_register_wait_cleanup(kn);
+       }
+}
+
+static int
+filt_wlvalidate_kev_flags(struct knote *kn, struct kevent_internal_s *kev,
+               thread_qos_t *qos_index)
+{
+       int new_commands = kev->fflags & NOTE_WL_COMMANDS_MASK;
+       int sav_commands = kn->kn_sfflags & NOTE_WL_COMMANDS_MASK;
+
+       if ((kev->fflags & NOTE_WL_DISCOVER_OWNER) && (kev->flags & EV_DELETE)) {
+               return EINVAL;
+       }
+       if (kev->fflags & NOTE_WL_UPDATE_QOS) {
+               if (kev->flags & EV_DELETE) {
+                       return EINVAL;
+               }
+               if (sav_commands != NOTE_WL_THREAD_REQUEST) {
+                       return EINVAL;
+               }
+               if (!(*qos_index = _pthread_priority_thread_qos(kev->qos))) {
+                       return ERANGE;
+               }
+       }
+
+       switch (new_commands) {
+       case NOTE_WL_THREAD_REQUEST:
+               /* thread requests can only update themselves */
+               if (sav_commands != NOTE_WL_THREAD_REQUEST)
+                       return EINVAL;
+               break;
+
+       case NOTE_WL_SYNC_WAIT:
+               if (kev->fflags & NOTE_WL_END_OWNERSHIP)
+                       return EINVAL;
+               goto sync_checks;
+
+       case NOTE_WL_SYNC_WAKE:
+       sync_checks:
+               if (!(sav_commands & (NOTE_WL_SYNC_WAIT | NOTE_WL_SYNC_WAKE)))
+                       return EINVAL;
+               if ((kev->flags & (EV_ENABLE | EV_DELETE)) == EV_ENABLE)
+                       return EINVAL;
+               break;
+
+       default:
+               return EINVAL;
+       }
+       return 0;
+}
+
+static int
+filt_wltouch(struct knote *kn, struct kevent_internal_s *kev)
+{
+       struct kqworkloop *kqwl = (struct kqworkloop *)knote_get_kq(kn);
+       thread_qos_t qos_index = THREAD_QOS_UNSPECIFIED;
+
+       int error = filt_wlvalidate_kev_flags(kn, kev, &qos_index);
+       if (error) {
+               goto out;
+       }
+
+       error = filt_wlupdate(kqwl, kn, kev, qos_index, FILT_WLTOUCH);
+       filt_wlremember_last_update(kn, kev, error);
+       if (error) {
+               goto out;
+       }
+
+out:
+       if (error) {
+               if (error == ESTALE && (kev->fflags & NOTE_WL_IGNORE_ESTALE)) {
+                       /* If userland wants ESTALE to be hidden, do not activate */
+                       return 0;
+               }
+               kev->flags |= EV_ERROR;
+               kev->data = error;
+               return 0;
+       }
+       int command = kev->fflags & NOTE_WL_COMMANDS_MASK;
+       if (command == NOTE_WL_SYNC_WAIT && !(kn->kn_sfflags & NOTE_WL_SYNC_WAKE)) {
+               return kevent_register_wait_prepare(kn, kev);
+       }
+       /* Just touching the thread request successfully will fire it */
+       if (command == NOTE_WL_THREAD_REQUEST) {
+               if (kev->fflags & NOTE_WL_UPDATE_QOS) {
+                       return FILTER_ACTIVE | FILTER_UPDATE_REQ_QOS;
+               }
+               return FILTER_ACTIVE;
+       }
+       return 0;
+}
+
+static bool
+filt_wlallow_drop(struct knote *kn, struct kevent_internal_s *kev)
+{
+       struct kqworkloop *kqwl = (struct kqworkloop *)knote_get_kq(kn);
+
+       int error = filt_wlvalidate_kev_flags(kn, kev, NULL);
+       if (error) {
+               goto out;
+       }
+
+       error = filt_wlupdate(kqwl, kn, kev, 0, FILT_WLDROP);
+       filt_wlremember_last_update(kn, kev, error);
+       if (error) {
+               goto out;
+       }
+
+out:
+       if (error) {
+               if (error == ESTALE && (kev->fflags & NOTE_WL_IGNORE_ESTALE)) {
+                       return false;
+               }
+               kev->flags |= EV_ERROR;
+               kev->data = error;
+               return false;
+       }
+       return true;
+}
+
+static int
+filt_wlprocess(
+       struct knote *kn,
+       __unused struct filt_process_s *data,
+       struct kevent_internal_s *kev)
+{
+       struct kqworkloop *kqwl = (struct kqworkloop *)knote_get_kq(kn);
+       int rc = 0;
+
+       assert(kn->kn_sfflags & NOTE_WL_THREAD_REQUEST);
+
+       filt_wllock(kqwl);
+
+       if (kqwl->kqwl_owner) {
+               /*
+                * <rdar://problem/33584321> userspace sometimes due to events being
+                * delivered but not triggering a drain session can cause a process
+                * of the thread request knote.
+                *
+                * When that happens, the automatic deactivation due to process
+                * would swallow the event, so we have to activate the knote again.
+                */
+               kqlock(kqwl);
+               knote_activate(kn);
+               kqunlock(kqwl);
+       } else {
+#if DEBUG || DEVELOPMENT
+               if (kevent_debug_flags() & KEVENT_PANIC_ON_NON_ENQUEUED_PROCESS) {
+                       /*
+                        * see src/queue_internal.h in libdispatch
+                        */
+#define DISPATCH_QUEUE_ENQUEUED 0x1ull
+                       user_addr_t addr = CAST_USER_ADDR_T(kn->kn_ext[EV_EXTIDX_WL_ADDR]);
+                       task_t t = current_task();
+                       uint64_t val;
+                       if (addr && task_is_active(t) && !task_is_halting(t) &&
+                                       copyin_word(addr, &val, sizeof(val)) == 0 &&
+                                       val && (val & DISPATCH_QUEUE_ENQUEUED) == 0 &&
+                                       (val >> 48) != 0xdead && (val >> 48) != 0 && (val >> 48) != 0xffff) {
+                               panic("kevent: workloop %#016llx is not enqueued "
+                                               "(kn:%p dq_state:%#016llx kev.dq_state:%#016llx)",
+                                               kn->kn_udata, kn, val, kn->kn_ext[EV_EXTIDX_WL_VALUE]);
+                       }
+               }
+#endif
+               *kev = kn->kn_kevent;
+               kev->fflags = kn->kn_sfflags;
+               kev->data = kn->kn_sdata;
+               kev->qos = kn->kn_qos;
+               rc |= FILTER_ACTIVE;
+       }
+
+       filt_wlunlock(kqwl);
+
+       if (rc & FILTER_ACTIVE) {
+               workq_thread_set_max_qos(kqwl->kqwl_p, &kqwl->kqwl_request);
+       }
+       return rc;
+}
+
+SECURITY_READ_ONLY_EARLY(static struct filterops) workloop_filtops = {
+       .f_extended_codes = true,
+       .f_attach  = filt_wlattach,
+       .f_detach  = filt_wldetach,
+       .f_event   = filt_badevent,
+       .f_touch   = filt_wltouch,
+       .f_process = filt_wlprocess,
+       .f_allow_drop = filt_wlallow_drop,
+       .f_post_register_wait = filt_wlpost_register_wait,
+};
+
+#pragma mark kevent / knotes
+
 /*
  * JMM - placeholder for not-yet-implemented filters
  */
 static int
-filt_badattach(__unused struct knote *kn)
+filt_badevent(struct knote *kn, long hint)
+{
+       panic("%s[%d](%p, %ld)", __func__, kn->kn_filter, kn, hint);
+       return 0;
+}
+
+static int
+filt_badattach(__unused struct knote *kn, __unused struct kevent_internal_s *kev)
 {
-       kn->kn_flags |= EV_ERROR;
-       kn->kn_data = ENOTSUP;
+       knote_set_error(kn, ENOTSUP);
        return 0;
 }
 
@@ -1616,8 +2514,7 @@ kqueue_alloc(struct proc *p, unsigned int flags)
        struct filedesc *fdp = p->p_fd;
        struct kqueue *kq = NULL;
        int policy;
-       void *hook;
-       uint64_t kq_addr_offset;
+       void *hook = NULL;
 
        if (flags & KEVENT_FLAG_WORKQ) {
                struct kqworkq *kqwq;
@@ -1633,35 +2530,71 @@ kqueue_alloc(struct proc *p, unsigned int flags)
                kqwq->kqwq_state = KQ_WORKQ;
 
                for (i = 0; i < KQWQ_NBUCKETS; i++) {
-                       TAILQ_INIT(&kq->kq_queue[i]);
+                       TAILQ_INIT(&kqwq->kqwq_queue[i]);
                }
-               for (i = 0; i < KQWQ_NQOS; i++) {
+               for (i = 0; i < KQWQ_NBUCKETS; i++) {
+                       if (i != KQWQ_QOS_MANAGER) {
+                               /*
+                                * Because of how the bucketized system works, we mix overcommit
+                                * sources with not overcommit: each time we move a knote from
+                                * one bucket to the next due to overrides, we'd had to track
+                                * overcommitness, and it's really not worth it in the workloop
+                                * enabled world that track this faithfully.
+                                *
+                                * Incidentally, this behaves like the original manager-based
+                                * kqwq where event delivery always happened (hence is
+                                * "overcommit")
+                                */
+                               kqwq->kqwq_request[i].kqr_state |= KQR_THOVERCOMMIT;
+                       }
+                       kqwq->kqwq_request[i].kqr_qos_index = i;
                        TAILQ_INIT(&kqwq->kqwq_request[i].kqr_suppressed);
                }
 
-               lck_spin_init(&kqwq->kqwq_reqlock, kq_lck_grp, kq_lck_attr);
                policy = SYNC_POLICY_FIFO;
                hook = (void *)kqwq;
-               
+       } else if (flags & KEVENT_FLAG_WORKLOOP) {
+               struct kqworkloop *kqwl;
+               int i;
+
+               kqwl = (struct kqworkloop *)zalloc(kqworkloop_zone);
+               if (kqwl == NULL)
+                       return NULL;
+
+               bzero(kqwl, sizeof (struct kqworkloop));
+
+               kqwl->kqwl_state = KQ_WORKLOOP | KQ_DYNAMIC;
+               kqwl->kqwl_retains = 1; /* donate a retain to creator */
+               kqwl->kqwl_request.kqr_state = KQR_WORKLOOP;
+
+               kq = &kqwl->kqwl_kqueue;
+               for (i = 0; i < KQWL_NBUCKETS; i++) {
+                       TAILQ_INIT(&kqwl->kqwl_queue[i]);
+               }
+               TAILQ_INIT(&kqwl->kqwl_request.kqr_suppressed);
+
+               lck_mtx_init(&kqwl->kqwl_statelock, kq_lck_grp, kq_lck_attr);
+
+               policy = SYNC_POLICY_FIFO;
+               hook = (void *)kqwl;
        } else {
                struct kqfile *kqf;
-               
+
                kqf = (struct kqfile *)zalloc(kqfile_zone);
                if (kqf == NULL)
                        return NULL;
 
                kq = &kqf->kqf_kqueue;
                bzero(kqf, sizeof (struct kqfile));
-               TAILQ_INIT(&kq->kq_queue[0]);
+               TAILQ_INIT(&kqf->kqf_queue);
                TAILQ_INIT(&kqf->kqf_suppressed);
-               
-               policy = SYNC_POLICY_FIFO | SYNC_POLICY_PREPOST;
-               hook = NULL;
 
+               policy = SYNC_POLICY_FIFO | SYNC_POLICY_PREPOST;
        }
 
        waitq_set_init(&kq->kq_wqs, policy, NULL, hook);
        lck_spin_init(&kq->kq_lock, kq_lck_grp, kq_lck_attr);
+       lck_spin_init(&kq->kq_reqlock, kq_lck_grp, kq_lck_attr);
        kq->kq_p = p;
 
        if (fdp->fd_knlistsize < 0) {
@@ -1671,16 +2604,109 @@ kqueue_alloc(struct proc *p, unsigned int flags)
                proc_fdunlock(p);
        }
 
-       kq_addr_offset = ((uintptr_t)kq - (uintptr_t)VM_MIN_KERNEL_AND_KEXT_ADDRESS);
-       /* Assert that the address can be pointer compacted for use with knote */
-       assert(kq_addr_offset < (uint64_t)(1ull << KNOTE_KQ_BITSIZE));
        return (kq);
 }
 
+/*
+ * knotes_dealloc - detach all knotes for the process and drop them
+ *
+ *             Called with proc_fdlock held.
+ *             Returns with it locked.
+ *             May drop it temporarily.
+ *             Process is in such a state that it will not try to allocate
+ *             any more knotes during this process (stopped for exit or exec).
+ */
+void
+knotes_dealloc(proc_t p)
+{
+       struct filedesc *fdp = p->p_fd;
+       struct kqueue *kq;
+       struct knote *kn;
+       struct  klist *kn_hash = NULL;
+       int i;
+
+       /* Close all the fd-indexed knotes up front */
+       if (fdp->fd_knlistsize > 0) {
+               for (i = 0; i < fdp->fd_knlistsize; i++) {
+                       while ((kn = SLIST_FIRST(&fdp->fd_knlist[i])) != NULL) {
+                               kq = knote_get_kq(kn);
+                               kqlock(kq);
+                               proc_fdunlock(p);
+                               knote_drop(kq, kn, NULL);
+                               proc_fdlock(p);
+                       }
+               }
+               /* free the table */
+               FREE(fdp->fd_knlist, M_KQUEUE);
+               fdp->fd_knlist = NULL;
+       }
+       fdp->fd_knlistsize = -1;
+
+       knhash_lock(p);
+       proc_fdunlock(p);
+
+       /* Clean out all the hashed knotes as well */
+       if (fdp->fd_knhashmask != 0) {
+               for (i = 0; i <= (int)fdp->fd_knhashmask; i++) {
+                       while ((kn = SLIST_FIRST(&fdp->fd_knhash[i])) != NULL) {
+                               kq = knote_get_kq(kn);
+                               kqlock(kq);
+                               knhash_unlock(p);
+                               knote_drop(kq, kn, NULL);
+                               knhash_lock(p);
+                       }
+               }
+               kn_hash = fdp->fd_knhash;
+               fdp->fd_knhashmask = 0;
+               fdp->fd_knhash = NULL;
+       }
+
+       knhash_unlock(p);
+
+       /* free the kn_hash table */
+       if (kn_hash)
+               FREE(kn_hash, M_KQUEUE);
+
+       proc_fdlock(p);
+}
+
+/*
+ * kqworkloop_invalidate
+ *
+ * Invalidate ownership of a workloop.
+ *
+ * This is meant to be used so that any remnant of overrides and ownership
+ * information is dropped before a kqworkloop can no longer be found in the
+ * global hash table and have ghost workloop ownership left over.
+ *
+ * Possibly returns a thread to deallocate in a safe context.
+ */
+static thread_t
+kqworkloop_invalidate(struct kqworkloop *kqwl)
+{
+       thread_t cur_owner = kqwl->kqwl_owner;
+
+       assert(TAILQ_EMPTY(&kqwl->kqwl_request.kqr_suppressed));
+       if (cur_owner) {
+               /*
+                * If the kqueue had an owner that prevented the thread request to
+                * go through, then no unbind happened, and we may have lingering
+                * overrides to drop.
+                */
+               if (kqworkloop_owner_override(kqwl) != THREAD_QOS_UNSPECIFIED) {
+                       thread_drop_ipc_override(cur_owner);
+               }
+               thread_ends_owning_workloop(cur_owner);
+               kqwl->kqwl_owner = THREAD_NULL;
+       }
+
+       return cur_owner;
+}
+
 /*
  * kqueue_dealloc - detach all knotes from a kqueue and free it
  *
- *     We walk each list looking for knotes referencing this
+ *     We walk each list looking for knotes referencing this
  *     this kqueue.  If we find one, we try to drop it.  But
  *     if we fail to get a drop reference, that will wait
  *     until it is dropped.  So, we can just restart again
@@ -1690,6 +2716,10 @@ kqueue_alloc(struct proc *p, unsigned int flags)
  *
  *     Assumes no new events are being added to the kqueue.
  *     Nothing locked on entry or exit.
+ *
+ * Workloop kqueues cant get here unless all the knotes
+ * are already gone and all requested threads have come
+ * and gone (cancelled or arrived).
  */
 void
 kqueue_dealloc(struct kqueue *kq)
@@ -1704,47 +2734,73 @@ kqueue_dealloc(struct kqueue *kq)
 
        p = kq->kq_p;
        fdp = p->p_fd;
-
-       proc_fdlock(p);
-       for (i = 0; i < fdp->fd_knlistsize; i++) {
-               kn = SLIST_FIRST(&fdp->fd_knlist[i]);
-               while (kn != NULL) {
-                       if (kq == knote_get_kq(kn)) {
-                               kqlock(kq);
-                               proc_fdunlock(p);
-                               /* drop it ourselves or wait */
-                               if (kqlock2knotedrop(kq, kn)) {
-                                       knote_drop(kn, p);
-                               }
-                               proc_fdlock(p);
-                               /* start over at beginning of list */
-                               kn = SLIST_FIRST(&fdp->fd_knlist[i]);
-                               continue;
-                       }
-                       kn = SLIST_NEXT(kn, kn_link);
-               }
-       }
-       if (fdp->fd_knhashmask != 0) {
-               for (i = 0; i < (int)fdp->fd_knhashmask + 1; i++) {
-                       kn = SLIST_FIRST(&fdp->fd_knhash[i]);
+
+       /*
+        * Workloops are refcounted by their knotes, so there's no point
+        * spending a lot of time under these locks just to deallocate one.
+        */
+       if ((kq->kq_state & KQ_WORKLOOP) == 0) {
+               KNOTE_LOCK_CTX(knlc);
+
+               proc_fdlock(p);
+               for (i = 0; i < fdp->fd_knlistsize; i++) {
+                       kn = SLIST_FIRST(&fdp->fd_knlist[i]);
                        while (kn != NULL) {
                                if (kq == knote_get_kq(kn)) {
                                        kqlock(kq);
                                        proc_fdunlock(p);
-                                       /* drop it ourselves or wait */
-                                       if (kqlock2knotedrop(kq, kn)) {
-                                               knote_drop(kn, p);
+                                       if (knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ON_SUCCESS)) {
+                                               knote_drop(kq, kn, &knlc);
                                        }
                                        proc_fdlock(p);
                                        /* start over at beginning of list */
-                                       kn = SLIST_FIRST(&fdp->fd_knhash[i]);
+                                       kn = SLIST_FIRST(&fdp->fd_knlist[i]);
                                        continue;
                                }
                                kn = SLIST_NEXT(kn, kn_link);
                        }
                }
+
+               knhash_lock(p);
+               proc_fdunlock(p);
+
+               if (fdp->fd_knhashmask != 0) {
+                       for (i = 0; i < (int)fdp->fd_knhashmask + 1; i++) {
+                               kn = SLIST_FIRST(&fdp->fd_knhash[i]);
+                               while (kn != NULL) {
+                                       if (kq == knote_get_kq(kn)) {
+                                               kqlock(kq);
+                                               knhash_unlock(p);
+                                               if (knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ON_SUCCESS)) {
+                                                       knote_drop(kq, kn, &knlc);
+                                               }
+                                               knhash_lock(p);
+                                               /* start over at beginning of list */
+                                               kn = SLIST_FIRST(&fdp->fd_knhash[i]);
+                                               continue;
+                                       }
+                                       kn = SLIST_NEXT(kn, kn_link);
+                               }
+                       }
+               }
+               knhash_unlock(p);
+       }
+
+       if (kq->kq_state & KQ_WORKLOOP) {
+               struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+               thread_t cur_owner = kqworkloop_invalidate(kqwl);
+
+               if (cur_owner) thread_deallocate(cur_owner);
+
+               if (kqwl->kqwl_request.kqr_state & KQR_ALLOCATED_TURNSTILE) {
+                       struct turnstile *ts;
+                       turnstile_complete((uintptr_t)kqwl, &kqwl->kqwl_turnstile, &ts);
+                       turnstile_cleanup();
+                       turnstile_deallocate(ts);
+               } else {
+                       assert(kqwl->kqwl_turnstile == NULL);
+               }
        }
-       proc_fdunlock(p);
 
        /*
         * waitq_set_deinit() remove the KQ's waitq set from
@@ -1752,17 +2808,57 @@ kqueue_dealloc(struct kqueue *kq)
         */
        waitq_set_deinit(&kq->kq_wqs);
        lck_spin_destroy(&kq->kq_lock, kq_lck_grp);
+       lck_spin_destroy(&kq->kq_reqlock, kq_lck_grp);
 
        if (kq->kq_state & KQ_WORKQ) {
-               struct kqworkq *kqwq = (struct kqworkq *)kq;
+               zfree(kqworkq_zone, (struct kqworkq *)kq);
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               struct kqworkloop *kqwl = (struct kqworkloop *)kq;
 
-               lck_spin_destroy(&kqwq->kqwq_reqlock, kq_lck_grp);
-               zfree(kqworkq_zone, kqwq);
+               assert(kqwl->kqwl_retains == 0);
+               lck_mtx_destroy(&kqwl->kqwl_statelock, kq_lck_grp);
+               zfree(kqworkloop_zone, kqwl);
        } else {
-               struct kqfile *kqf = (struct kqfile *)kq;
+               zfree(kqfile_zone, (struct kqfile *)kq);
+       }
+}
+
+static inline void
+kqueue_retain(struct kqueue *kq)
+{
+       struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+       uint32_t previous;
+
+       if ((kq->kq_state & KQ_DYNAMIC) == 0)
+               return;
+
+       previous = OSIncrementAtomic(&kqwl->kqwl_retains);
+       if (previous == KQ_WORKLOOP_RETAINS_MAX)
+               panic("kq(%p) retain overflow", kq);
+
+       if (previous == 0)
+               panic("kq(%p) resurrection", kq);
+}
+
+#define KQUEUE_CANT_BE_LAST_REF  0
+#define KQUEUE_MIGHT_BE_LAST_REF 1
 
-               zfree(kqfile_zone, kqf);
+static inline int
+kqueue_release(kqueue_t kqu, __assert_only int possibly_last)
+{
+       if ((kqu.kq->kq_state & KQ_DYNAMIC) == 0) {
+               return 0;
+       }
+
+       assert(kqu.kq->kq_state & KQ_WORKLOOP); /* for now */
+       uint32_t refs = OSDecrementAtomic(&kqu.kqwl->kqwl_retains);
+       if (__improbable(refs == 0)) {
+               panic("kq(%p) over-release", kqu.kq);
        }
+       if (refs == 1) {
+               assert(possibly_last);
+       }
+       return refs == 1;
 }
 
 int
@@ -1806,7 +2902,7 @@ kqueue(struct proc *p, __unused struct kqueue_args *uap, int32_t *retval)
 
 static int
 kevent_copyin(user_addr_t *addrp, struct kevent_internal_s *kevp, struct proc *p,
-    unsigned int flags)
+               unsigned int flags)
 {
        int advance;
        int error;
@@ -1858,7 +2954,7 @@ kevent_copyin(user_addr_t *addrp, struct kevent_internal_s *kevp, struct proc *p
                kevp->data = kev64.data;
                kevp->ext[0] = kev64.ext[0];
                kevp->ext[1] = kev64.ext[1];
-               
+
        } else {
                struct kevent_qos_s kevqos;
 
@@ -1888,13 +2984,13 @@ kevent_copyin(user_addr_t *addrp, struct kevent_internal_s *kevp, struct proc *p
 
 static int
 kevent_copyout(struct kevent_internal_s *kevp, user_addr_t *addrp, struct proc *p,
-    unsigned int flags)
+               unsigned int flags)
 {
        user_addr_t addr = *addrp;
        int advance;
        int error;
 
-       /* 
+       /*
         * fully initialize the differnt output event structure
         * types from the internal kevent (and some universal
         * defaults for fields not represented in the internal
@@ -1908,7 +3004,7 @@ kevent_copyout(struct kevent_internal_s *kevp, user_addr_t *addrp, struct proc *
 
                        advance = sizeof (kev64);
                        bzero(&kev64, advance);
-                       
+
                        /*
                         * deal with the special case of a user-supplied
                         * value of (uintptr_t)-1.
@@ -1954,7 +3050,7 @@ kevent_copyout(struct kevent_internal_s *kevp, user_addr_t *addrp, struct proc *
                error = copyout((caddr_t)&kev64, addr, advance);
        } else {
                struct kevent_qos_s kevqos;
-          
+
                advance = sizeof (struct kevent_qos_s);
                if (flags & KEVENT_FLAG_STACK_EVENTS) {
                        addr -= advance;
@@ -1984,10 +3080,11 @@ kevent_copyout(struct kevent_internal_s *kevp, user_addr_t *addrp, struct proc *
 }
 
 static int
-kevent_get_data_size(struct proc *p, 
-                     uint64_t data_available,
-                     unsigned int flags,
-                     user_size_t *residp)
+kevent_get_data_size(
+               struct proc *p,
+               uint64_t data_available,
+               unsigned int flags,
+               user_size_t *residp)
 {
        user_size_t resid;
        int error = 0;
@@ -2014,10 +3111,11 @@ kevent_get_data_size(struct proc *p,
 }
 
 static int
-kevent_put_data_size(struct proc *p, 
-                     uint64_t data_available,
-                     unsigned int flags,
-                     user_size_t resid)
+kevent_put_data_size(
+               struct proc *p,
+               uint64_t data_available,
+               unsigned int flags,
+               user_size_t resid)
 {
        int error = 0;
 
@@ -2040,7 +3138,6 @@ kevent_put_data_size(struct proc *p,
  *
  *     assume we inherit a use count on the kq fileglob.
  */
-
 __attribute__((noreturn))
 static void
 kevent_continue(__unused struct kqueue *kq, void *data, int error)
@@ -2066,8 +3163,7 @@ kevent_continue(__unused struct kqueue *kq, void *data, int error)
        fd = cont_args->fd;
        fp = cont_args->fp;
 
-       if (fp != NULL)
-               fp_drop(p, fd, fp, 0);
+       kevent_put_kq(p, fd, fp, kq);
 
        /* don't abandon other output just because of residual copyout failures */
        if (error == 0 && data_available && data_resid != data_size) {
@@ -2094,7 +3190,7 @@ kevent(struct proc *p, struct kevent_args *uap, int32_t *retval)
        unsigned int flags = KEVENT_FLAG_LEGACY32;
 
        return kevent_internal(p,
-                              uap->fd,
+                              (kqueue_id_t)uap->fd, NULL,
                               uap->changelist, uap->nchanges,
                               uap->eventlist, uap->nevents,
                               0ULL, 0ULL,
@@ -2114,7 +3210,7 @@ kevent64(struct proc *p, struct kevent64_args *uap, int32_t *retval)
        flags |= KEVENT_FLAG_LEGACY64;
 
        return kevent_internal(p,
-                              uap->fd,
+                              (kqueue_id_t)uap->fd, NULL,
                               uap->changelist, uap->nchanges,
                               uap->eventlist, uap->nevents,
                               0ULL, 0ULL,
@@ -2131,7 +3227,7 @@ kevent_qos(struct proc *p, struct kevent_qos_args *uap, int32_t *retval)
        uap->flags &= KEVENT_FLAG_USER;
 
        return kevent_internal(p,
-                              uap->fd,
+                              (kqueue_id_t)uap->fd, NULL,
                               uap->changelist, uap->nchanges,
                               uap->eventlist,  uap->nevents,
                               uap->data_out, (uint64_t)uap->data_available,
@@ -2141,16 +3237,16 @@ kevent_qos(struct proc *p, struct kevent_qos_args *uap, int32_t *retval)
                               retval);
 }
 
-int 
-kevent_qos_internal(struct proc *p, int fd, 
+int
+kevent_qos_internal(struct proc *p, int fd,
                    user_addr_t changelist, int nchanges,
                    user_addr_t eventlist, int nevents,
                    user_addr_t data_out, user_size_t *data_available,
-                   unsigned int flags, 
-                   int32_t *retval) 
+                   unsigned int flags,
+                   int32_t *retval)
 {
        return kevent_internal(p,
-                              fd,
+                              (kqueue_id_t)fd, NULL,
                               changelist, nchanges,
                               eventlist, nevents,
                               data_out, (uint64_t)data_available,
@@ -2159,7 +3255,43 @@ kevent_qos_internal(struct proc *p, int fd,
                               NULL,
                               retval);
 }
+
+int
+kevent_id(struct proc *p, struct kevent_id_args *uap, int32_t *retval)
+{
+       /* restrict to user flags */
+       uap->flags &= KEVENT_FLAG_USER;
+
+       return kevent_internal(p,
+                              (kqueue_id_t)uap->id, NULL,
+                              uap->changelist, uap->nchanges,
+                              uap->eventlist,  uap->nevents,
+                              uap->data_out, (uint64_t)uap->data_available,
+                              (uap->flags | KEVENT_FLAG_DYNAMIC_KQUEUE),
+                              0ULL,
+                              kevent_continue,
+                              retval);
+}
+
+int
+kevent_id_internal(struct proc *p, kqueue_id_t *id,
+                   user_addr_t changelist, int nchanges,
+                   user_addr_t eventlist, int nevents,
+                   user_addr_t data_out, user_size_t *data_available,
+                   unsigned int flags,
+                   int32_t *retval)
+{
+       return kevent_internal(p,
+                              *id, id,
+                              changelist, nchanges,
+                              eventlist, nevents,
+                              data_out, (uint64_t)data_available,
+                              (flags | KEVENT_FLAG_KERNEL | KEVENT_FLAG_DYNAMIC_KQUEUE),
+                              0ULL,
+                              NULL,
+                              retval);
+}
+
 static int
 kevent_get_timeout(struct proc *p,
                   user_addr_t utimeout,
@@ -2220,46 +3352,361 @@ kevent_set_kq_mode(struct kqueue *kq, unsigned int flags)
                }
        } else if (flags & KEVENT_FLAG_LEGACY32) {
                kq->kq_state |= KQ_KEV32;
-       } else {
-               /* JMM - set KQ_KEVQOS when we are ready for exclusive */
+       } else if (flags & KEVENT_FLAG_LEGACY64) {
                kq->kq_state |= KQ_KEV64;
+       } else {
+               kq->kq_state |= KQ_KEV_QOS;
        }
        kqunlock(kq);
        return 0;
 }
 
+#define        KQ_HASH(val, mask)  (((val) ^ (val >> 8)) & (mask))
+#define CONFIG_KQ_HASHSIZE  CONFIG_KN_HASHSIZE
+
+static inline void
+kqhash_lock(proc_t p)
+{
+       lck_mtx_lock_spin_always(&p->p_fd->fd_kqhashlock);
+}
+
+static inline void
+kqhash_lock_held(__assert_only proc_t p)
+{
+       LCK_MTX_ASSERT(&p->p_fd->fd_kqhashlock, LCK_MTX_ASSERT_OWNED);
+}
+
+static inline void
+kqhash_unlock(proc_t p)
+{
+       lck_mtx_unlock(&p->p_fd->fd_kqhashlock);
+}
+
+static void
+kqueue_hash_init_if_needed(proc_t p)
+{
+       struct filedesc *fdp = p->p_fd;
+
+       kqhash_lock_held(p);
+
+       if (__improbable(fdp->fd_kqhash == NULL)) {
+               struct kqlist *alloc_hash;
+               u_long alloc_mask;
+
+               kqhash_unlock(p);
+               alloc_hash = hashinit(CONFIG_KQ_HASHSIZE, M_KQUEUE, &alloc_mask);
+               kqhash_lock(p);
+
+               /* See if we won the race */
+               if (fdp->fd_kqhashmask == 0) {
+                       fdp->fd_kqhash = alloc_hash;
+                       fdp->fd_kqhashmask = alloc_mask;
+               } else {
+                       kqhash_unlock(p);
+                       FREE(alloc_hash, M_KQUEUE);
+                       kqhash_lock(p);
+               }
+       }
+}
+
+/*
+ * Called with the kqhash_lock() held
+ */
+static void
+kqueue_hash_insert(
+       struct proc *p,
+       kqueue_id_t id,
+       struct kqueue *kq)
+{
+       struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+       struct filedesc *fdp = p->p_fd;
+       struct kqlist *list;
+
+       /* should hold the kq hash lock */
+       kqhash_lock_held(p);
+
+       if ((kq->kq_state & KQ_DYNAMIC) == 0) {
+               assert(kq->kq_state & KQ_DYNAMIC);
+               return;
+       }
+
+       /* only dynamically allocate workloop kqs for now */
+       assert(kq->kq_state & KQ_WORKLOOP);
+       assert(fdp->fd_kqhash);
+
+       kqwl->kqwl_dynamicid = id;
+
+       list = &fdp->fd_kqhash[KQ_HASH(id, fdp->fd_kqhashmask)];
+       SLIST_INSERT_HEAD(list, kqwl, kqwl_hashlink);
+}
+
+/* Called with kqhash_lock held */
+static void
+kqueue_hash_remove(
+       struct proc *p,
+       struct kqueue *kq)
+{
+       struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+       struct filedesc *fdp = p->p_fd;
+       struct kqlist *list;
+
+       /* should hold the kq hash lock */
+       kqhash_lock_held(p);
+
+       if ((kq->kq_state & KQ_DYNAMIC) == 0) {
+               assert(kq->kq_state & KQ_DYNAMIC);
+               return;
+       }
+       assert(kq->kq_state & KQ_WORKLOOP); /* for now */
+       list = &fdp->fd_kqhash[KQ_HASH(kqwl->kqwl_dynamicid, fdp->fd_kqhashmask)];
+       SLIST_REMOVE(list, kqwl, kqworkloop, kqwl_hashlink);
+}
+
+/* Called with kqhash_lock held */
+static struct kqueue *
+kqueue_hash_lookup(struct proc *p, kqueue_id_t id)
+{
+       struct filedesc *fdp = p->p_fd;
+       struct kqlist *list;
+       struct kqworkloop *kqwl;
+
+       /* should hold the kq hash lock */
+       kqhash_lock_held(p);
+
+       if (fdp->fd_kqhashmask == 0) return NULL;
+
+       list = &fdp->fd_kqhash[KQ_HASH(id, fdp->fd_kqhashmask)];
+       SLIST_FOREACH(kqwl, list, kqwl_hashlink) {
+               if (kqwl->kqwl_dynamicid == id) {
+                       struct kqueue *kq = (struct kqueue *)kqwl;
+
+                       assert(kq->kq_state & KQ_DYNAMIC);
+                       assert(kq->kq_state & KQ_WORKLOOP); /* for now */
+                       return kq;
+               }
+       }
+       return NULL;
+}
+
+static inline void
+kqueue_release_last(struct proc *p, kqueue_t kqu)
+{
+       struct kqueue *kq = kqu.kq;
+       if (kq->kq_state & KQ_DYNAMIC) {
+               kqhash_lock(p);
+               if (kqueue_release(kq, KQUEUE_MIGHT_BE_LAST_REF)) {
+                       thread_t cur_owner = kqworkloop_invalidate(kqu.kqwl);
+                       kqueue_hash_remove(p, kq);
+                       kqhash_unlock(p);
+                       if (cur_owner) thread_deallocate(cur_owner);
+                       kqueue_dealloc(kq);
+               } else {
+                       kqhash_unlock(p);
+               }
+       }
+}
+
+/*
+ * kqworkloops_dealloc - rebalance retains on kqworkloops created with
+ * scheduling parameters
+ *
+ *             Called with proc_fdlock held.
+ *             Returns with it locked.
+ *             Process is in such a state that it will not try to allocate
+ *             any more knotes during this process (stopped for exit or exec).
+ */
+void
+kqworkloops_dealloc(proc_t p)
+{
+       struct filedesc *fdp = p->p_fd;
+       struct kqlist *list;
+       struct kqworkloop *kqwl, *kqwln;
+       struct kqlist tofree;
+       int i;
+
+       if (!(fdp->fd_flags & FD_WORKLOOP)) {
+               return;
+       }
+
+       SLIST_INIT(&tofree);
+
+       kqhash_lock(p);
+       assert(fdp->fd_kqhashmask != 0);
+
+       for (i = 0; i <= (int)fdp->fd_kqhashmask; i++) {
+               list = &fdp->fd_kqhash[i];
+               SLIST_FOREACH_SAFE(kqwl, list, kqwl_hashlink, kqwln) {
+                       /*
+                        * kqworkloops that have scheduling parameters have an
+                        * implicit retain from kqueue_workloop_ctl that needs
+                        * to be balanced on process exit.
+                        */
+                       assert(kqwl->kqwl_params);
+                       SLIST_REMOVE(list, kqwl, kqworkloop, kqwl_hashlink);
+                       SLIST_INSERT_HEAD(&tofree, kqwl, kqwl_hashlink);
+               }
+       }
+
+       kqhash_unlock(p);
+
+       SLIST_FOREACH_SAFE(kqwl, &tofree, kqwl_hashlink, kqwln) {
+               struct kqueue *kq = (struct kqueue *)kqwl;
+               __assert_only bool released;
+               released = kqueue_release(kq, KQUEUE_MIGHT_BE_LAST_REF);
+               assert(released);
+               kqueue_dealloc(kq);
+       }
+}
+
+static struct kqueue *
+kevent_get_bound_kqworkloop(thread_t thread)
+{
+       struct uthread *ut = get_bsdthread_info(thread);
+       struct kqrequest *kqr = ut->uu_kqr_bound;
+
+       return kqr ? (struct kqueue *)kqr_kqworkloop(kqr) : NULL;
+}
+
 static int
-kevent_get_kq(struct proc *p, int fd, unsigned int flags, struct fileproc **fpp, struct kqueue **kqp)
+kevent_get_kq(struct proc *p, kqueue_id_t id, workq_threadreq_param_t *trp,
+               unsigned int flags, struct fileproc **fpp, int *fdp,
+               struct kqueue **kqp)
 {
+       struct filedesc *descp = p->p_fd;
        struct fileproc *fp = NULL;
-       struct kqueue *kq;
-       int error;
+       struct kqueue *kq = NULL;
+       int fd = 0;
+       int error = 0;
+       thread_t th = current_thread();
+
+       assert(!trp || (flags & KEVENT_FLAG_WORKLOOP));
+
+       /* Was the workloop flag passed?  Then it is for sure only a workloop */
+       if (flags & KEVENT_FLAG_DYNAMIC_KQUEUE) {
+               assert(flags & KEVENT_FLAG_WORKLOOP);
+               assert(!trp || (flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST));
+               kq = kevent_get_bound_kqworkloop(th);
+
+               /*
+                * when kevent_id_internal is called from within the
+                * kernel, and the passed 'id' value is '-1' then we
+                * look for the currently bound workloop kq.
+                */
+               if (id == (kqueue_id_t)-1 &&
+                   (flags & KEVENT_FLAG_KERNEL) &&
+                   (flags & KEVENT_FLAG_WORKLOOP)) {
+
+                       if (!is_workqueue_thread(th) || !kq) {
+                               return EINVAL;
+                       }
+
+                       kqueue_retain(kq);
+                       goto out;
+               }
+
+               if (id == 0 || id == (kqueue_id_t)-1) {
+                       return EINVAL;
+               }
+
+               /* try shortcut on kq lookup for bound threads */
+               if (kq != NULL && ((struct kqworkloop *)kq)->kqwl_dynamicid == id) {
+
+                       if (flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST) {
+                               return EEXIST;
+                       }
+
+                       /* retain a reference while working with this kq. */
+                       assert(kq->kq_state & KQ_DYNAMIC);
+                       kqueue_retain(kq);
+                       goto out;
+               }
+
+               /* look for the kq on the hash table */
+               kqhash_lock(p);
+               kq = kqueue_hash_lookup(p, id);
+               if (kq == NULL) {
+                       kqhash_unlock(p);
+
+                       if (flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_EXIST) {
+                               return ENOENT;
+                       }
+
+                       struct kqueue *alloc_kq;
+                       alloc_kq = kqueue_alloc(p, flags);
+                       if (!alloc_kq) {
+                               return ENOMEM;
+                       }
+
+                       kqhash_lock(p);
+                       kqueue_hash_init_if_needed(p);
+                       kq = kqueue_hash_lookup(p, id);
+                       if (kq == NULL) {
+                               /* insert our new one */
+                               kq = alloc_kq;
+                               if (trp) {
+                                       struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+                                       kqwl->kqwl_params = trp->trp_value;
+                               }
+                               kqueue_hash_insert(p, id, kq);
+                               kqhash_unlock(p);
+                       } else if (flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST) {
+                               /* lost race and caller wants an error */
+                               kqhash_unlock(p);
+                               kqueue_release(alloc_kq, KQUEUE_MIGHT_BE_LAST_REF);
+                               kqueue_dealloc(alloc_kq);
+                               return EEXIST;
+                       } else {
+                               /* lost race, retain existing workloop */
+                               kqueue_retain(kq);
+                               kqhash_unlock(p);
+                               kqueue_release(alloc_kq, KQUEUE_MIGHT_BE_LAST_REF);
+                               kqueue_dealloc(alloc_kq);
+                       }
+               } else {
+
+                       if (flags & KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST) {
+                               kqhash_unlock(p);
+                               return  EEXIST;
+                       }
+
+                       /* retain a reference while working with this kq. */
+                       assert(kq->kq_state & KQ_DYNAMIC);
+                       kqueue_retain(kq);
+                       kqhash_unlock(p);
+               }
+
+       } else if (flags & KEVENT_FLAG_WORKQ) {
+               /* must already exist for bound threads. */
+               if (flags & KEVENT_FLAG_KERNEL) {
+                       assert(descp->fd_wqkqueue != NULL);
+               }
 
-       if (flags & KEVENT_FLAG_WORKQ) {
                /*
                 * use the private kq associated with the proc workq.
                 * Just being a thread within the process (and not
                 * being the exit/exec thread) is enough to hold a
                 * reference on this special kq.
                 */
-               kq = p->p_wqkqueue;
+               kq = descp->fd_wqkqueue;
                if (kq == NULL) {
                        struct kqueue *alloc_kq = kqueue_alloc(p, KEVENT_FLAG_WORKQ);
-                       if (alloc_kq == NULL)
+                       if (alloc_kq == NULL) {
                                return ENOMEM;
+                       }
 
-                       proc_fdlock(p);
-                       if (p->p_wqkqueue == NULL) {
-                               kq = p->p_wqkqueue = alloc_kq;
-                               proc_fdunlock(p);
+                       knhash_lock(p);
+                       if (descp->fd_wqkqueue == NULL) {
+                               kq = descp->fd_wqkqueue = alloc_kq;
+                               knhash_unlock(p);
                        } else {
-                               proc_fdunlock(p);
-                               kq = p->p_wqkqueue;
+                               knhash_unlock(p);
+                               kq = descp->fd_wqkqueue;
                                kqueue_dealloc(alloc_kq);
                        }
                }
        } else {
                /* get a usecount for the kq itself */
+               fd = (int)id;
                if ((error = fp_getfkq(p, fd, &fp, &kq)) != 0)
                        return (error);
        }
@@ -2268,43 +3715,176 @@ kevent_get_kq(struct proc *p, int fd, unsigned int flags, struct fileproc **fpp,
                if (fp != NULL)
                        fp_drop(p, fd, fp, 0);
                return error;
-       } 
+       }
 
+out:
        *fpp = fp;
+       *fdp = fd;
        *kqp = kq;
+
+       return error;
+}
+
+static void
+kevent_put_kq(
+       struct proc *p,
+       kqueue_id_t id,
+       struct fileproc *fp,
+       struct kqueue *kq)
+{
+       kqueue_release_last(p, kq);
+       if (fp != NULL) {
+               assert((kq->kq_state & KQ_WORKQ) == 0);
+               fp_drop(p, (int)id, fp, 0);
+       }
+}
+
+static uint64_t
+kevent_workloop_serial_no_copyin(proc_t p, uint64_t workloop_id)
+{
+       uint64_t serial_no = 0;
+       user_addr_t addr;
+       int rc;
+
+       if (workloop_id == 0 || p->p_dispatchqueue_serialno_offset == 0) {
+               return 0;
+       }
+       addr = (user_addr_t)(workloop_id + p->p_dispatchqueue_serialno_offset);
+
+       if (proc_is64bit(p)) {
+               rc = copyin(addr, (caddr_t)&serial_no, sizeof(serial_no));
+       } else {
+               uint32_t serial_no32 = 0;
+               rc = copyin(addr, (caddr_t)&serial_no32, sizeof(serial_no32));
+               serial_no = serial_no32;
+       }
+       return rc == 0 ? serial_no : 0;
+}
+
+int
+kevent_exit_on_workloop_ownership_leak(thread_t thread)
+{
+       proc_t p = current_proc();
+       struct filedesc *fdp = p->p_fd;
+       kqueue_id_t workloop_id = 0;
+       os_reason_t reason = OS_REASON_NULL;
+       mach_vm_address_t addr;
+       uint32_t reason_size;
+
+       kqhash_lock(p);
+       if (fdp->fd_kqhashmask > 0) {
+               for (uint32_t i = 0; i < fdp->fd_kqhashmask + 1; i++) {
+                       struct kqworkloop *kqwl;
+
+                       SLIST_FOREACH(kqwl, &fdp->fd_kqhash[i], kqwl_hashlink) {
+                               struct kqueue *kq = &kqwl->kqwl_kqueue;
+                               if ((kq->kq_state & KQ_DYNAMIC) && kqwl->kqwl_owner == thread) {
+                                       workloop_id = kqwl->kqwl_dynamicid;
+                                       break;
+                               }
+                       }
+               }
+       }
+       kqhash_unlock(p);
+
+       reason = os_reason_create(OS_REASON_LIBSYSTEM,
+                       OS_REASON_LIBSYSTEM_CODE_WORKLOOP_OWNERSHIP_LEAK);
+       if (reason == OS_REASON_NULL) {
+               goto out;
+       }
+
+       reason->osr_flags |= OS_REASON_FLAG_GENERATE_CRASH_REPORT;
+       reason_size = 2 * sizeof(uint64_t);
+       reason_size = kcdata_estimate_required_buffer_size(2, reason_size);
+       if (os_reason_alloc_buffer(reason, reason_size) != 0) {
+               goto out;
+       }
+
+       if (workloop_id) {
+               struct kcdata_descriptor *kcd = &reason->osr_kcd_descriptor;
+
+               if (kcdata_get_memory_addr(kcd, EXIT_REASON_WORKLOOP_ID,
+                               sizeof(workloop_id), &addr) == KERN_SUCCESS) {
+                       kcdata_memcpy(kcd, addr, &workloop_id, sizeof(workloop_id));
+               }
+
+               uint64_t serial_no = kevent_workloop_serial_no_copyin(p, workloop_id);
+               if (serial_no && kcdata_get_memory_addr(kcd, EXIT_REASON_DISPATCH_QUEUE_NO,
+                               sizeof(serial_no), &addr) == KERN_SUCCESS) {
+                       kcdata_memcpy(kcd, addr, &serial_no, sizeof(serial_no));
+               }
+       }
+out:
+#if DEVELOPMENT || DEBUG
+       if (kevent_debug_flags() & KEVENT_PANIC_ON_WORKLOOP_OWNERSHIP_LEAK) {
+               panic("thread %p in task %p is leaked workloop 0x%016llx ownership",
+                               thread, p->task, workloop_id);
+       }
+       psignal_try_thread_with_reason(p, thread, SIGABRT, reason);
        return 0;
+#else
+       return exit_with_reason(p, W_EXITCODE(0, SIGKILL), (int *)NULL,
+                       FALSE, FALSE, 0, reason);
+#endif
 }
 
+static inline boolean_t
+kevent_args_requesting_events(unsigned int flags, int nevents)
+{
+       return (!(flags & KEVENT_FLAG_ERROR_EVENTS) && nevents > 0);
+}
 
 static int
-kevent_internal(struct proc *p, 
-               int fd,
+kevent_internal(struct proc *p,
+               kqueue_id_t id, kqueue_id_t *id_out,
                user_addr_t changelist, int nchanges,
                user_addr_t ueventlist, int nevents,
                user_addr_t data_out, uint64_t data_available,
-               unsigned int flags, 
+               unsigned int flags,
                user_addr_t utimeout,
                kqueue_continue_t continuation,
                int32_t *retval)
 {
-       struct _kevent *cont_args;
        uthread_t ut;
        struct kqueue *kq;
        struct fileproc *fp = NULL;
+       int fd = 0;
        struct kevent_internal_s kev;
-       int error, noutputs;
+       int error, noutputs, register_rc;
+       bool needs_end_processing = false;
        struct timeval atv;
        user_size_t data_size;
        user_size_t data_resid;
+       thread_t thread = current_thread();
+       KNOTE_LOCK_CTX(knlc);
+
+       /* Don't allow user-space threads to process output events from the workq kqs */
+       if (((flags & (KEVENT_FLAG_WORKQ | KEVENT_FLAG_KERNEL)) == KEVENT_FLAG_WORKQ) &&
+           kevent_args_requesting_events(flags, nevents))
+               return EINVAL;
+
+       if (flags & KEVENT_FLAG_PARKING) {
+               if (!kevent_args_requesting_events(flags, nevents) || id != (kqueue_id_t)-1)
+                       return EINVAL;
+       }
+
+       /* restrict dynamic kqueue allocation to workloops (for now) */
+       if ((flags & (KEVENT_FLAG_DYNAMIC_KQUEUE | KEVENT_FLAG_WORKLOOP)) == KEVENT_FLAG_DYNAMIC_KQUEUE)
+               return EINVAL;
 
-       /* Don't allow user-space threads to process output events from the workq kq */
-       if ((flags & (KEVENT_FLAG_WORKQ | KEVENT_FLAG_KERNEL)) == KEVENT_FLAG_WORKQ &&
-           !(flags & KEVENT_FLAG_ERROR_EVENTS) && nevents > 0)
+       if ((flags & (KEVENT_FLAG_WORKLOOP)) && (flags & (KEVENT_FLAG_WORKQ)))
                return EINVAL;
 
+       if (flags & (KEVENT_FLAG_DYNAMIC_KQ_MUST_EXIST | KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST)) {
+
+               /* allowed only on workloops when calling kevent_id from user-space */
+               if (!(flags & KEVENT_FLAG_WORKLOOP) || (flags & KEVENT_FLAG_KERNEL) || !(flags & KEVENT_FLAG_DYNAMIC_KQUEUE))
+                       return EINVAL;
+       }
+
        /* prepare to deal with stack-wise allocation of out events */
        if (flags & KEVENT_FLAG_STACK_EVENTS) {
-               int scale = ((flags & KEVENT_FLAG_LEGACY32) ? 
+               int scale = ((flags & KEVENT_FLAG_LEGACY32) ?
                             (IS_64BIT_PROCESS(p) ? sizeof(struct user64_kevent) :
                                                    sizeof(struct user32_kevent)) :
                             ((flags & KEVENT_FLAG_LEGACY64) ? sizeof(struct kevent64_s) :
@@ -2316,17 +3896,58 @@ kevent_internal(struct proc *p,
        error = kevent_get_timeout(p, utimeout, flags, &atv);
        if (error)
                return error;
-       
+
        /* copyin initial value of data residual from data_available */
        error = kevent_get_data_size(p, data_available, flags, &data_size);
        if (error)
                return error;
 
        /* get the kq we are going to be working on */
-       error = kevent_get_kq(p, fd, flags, &fp, &kq);
+       error = kevent_get_kq(p, id, NULL, flags, &fp, &fd, &kq);
+#if CONFIG_WORKLOOP_DEBUG
+       ut = (uthread_t)get_bsdthread_info(thread);
+       UU_KEVENT_HISTORY_WRITE_ENTRY(ut, {
+               .uu_kqid = id,
+               .uu_kq = error ? NULL : kq,
+               .uu_error = error,
+               .uu_nchanges = nchanges,
+               .uu_nevents = nevents,
+               .uu_flags = flags,
+       });
+#endif // CONFIG_WORKLOOP_DEBUG
        if (error)
                return error;
 
+       /* only bound threads can receive events on workloops */
+       if (flags & KEVENT_FLAG_WORKLOOP) {
+               struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+               struct kqrequest *kqr = &kqwl->kqwl_request;
+
+               assert(kq->kq_state & KQ_WORKLOOP);
+
+               if (kevent_args_requesting_events(flags, nevents)) {
+                       if (kq != kevent_get_bound_kqworkloop(thread)) {
+                               error = EXDEV;
+                               goto out;
+                       }
+
+                       kq_req_lock(kqwl);
+                       /*
+                        * Disable the R2K notification while doing a register, if the
+                        * caller wants events too, we don't want the AST to be set if we
+                        * will process these events soon.
+                        */
+                       kqr->kqr_state &= ~KQR_R2K_NOTIF_ARMED;
+                       needs_end_processing = true;
+                       kq_req_unlock(kq);
+               }
+
+               if (id_out) {
+                       *id_out = kqwl->kqwl_dynamicid;
+               }
+
+       }
+
        /* register all the change requests the user provided... */
        noutputs = 0;
        while (nchanges > 0 && error == 0) {
@@ -2337,11 +3958,43 @@ kevent_internal(struct proc *p,
                /* Make sure user doesn't pass in any system flags */
                kev.flags &= ~EV_SYSFLAGS;
 
-               kevent_register(kq, &kev, p);
+               register_rc = kevent_register(kq, &kev, &knlc);
+               if (register_rc & FILTER_REGISTER_WAIT) {
+                       kqlock_held(kq);
+
+                       // f_post_register_wait is meant to call a continuation and not to
+                       // return, which is why we don't support FILTER_REGISTER_WAIT if
+                       // KEVENT_FLAG_ERROR_EVENTS is not passed, or if the event that
+                       // waits isn't the last.
+                       //
+                       // It is implementable, but not used by any userspace code at the
+                       // moment, so for now return ENOTSUP if someone tries to do it.
+                       if (nchanges == 1 && nevents >= 1 && (flags & KEVENT_FLAG_ERROR_EVENTS)) {
+                               struct _kevent_register *cont_args;
+                               /* store the continuation/completion data in the uthread */
+                               ut = (uthread_t)get_bsdthread_info(thread);
+                               cont_args = &ut->uu_save.uus_kevent_register;
+                               cont_args->kev = kev;
+                               cont_args->kq = kq;
+                               cont_args->fp = fp;
+                               cont_args->fd = fd;
+                               cont_args->ueventlist = ueventlist;
+                               cont_args->flags = flags;
+                               cont_args->retval = retval;
+                               cont_args->eventcount = nevents;
+                               cont_args->eventout = noutputs;
+                               knote_fops(cont_args->knote)->f_post_register_wait(ut, &knlc, cont_args);
+                               panic("f_post_register_wait returned (kev: %p)", &kev);
+                       }
+
+                       kev.flags |= EV_ERROR;
+                       kev.data = ENOTSUP;
+                       knote_unlock(kq, knlc.knlc_knote, &knlc, KNOTE_KQ_UNLOCK);
+               }
 
-               if (nevents > 0 &&
-                   ((kev.flags & EV_ERROR) || (kev.flags & EV_RECEIPT))) {
-                       if (kev.flags & EV_RECEIPT) {
+               // keep in sync with kevent_register_wait_return()
+               if (nevents > 0 && (kev.flags & (EV_ERROR|EV_RECEIPT))) {
+                       if ((kev.flags & EV_ERROR) == 0) {
                                kev.flags |= EV_ERROR;
                                kev.data = 0;
                        }
@@ -2362,10 +4015,10 @@ kevent_internal(struct proc *p,
 
        /* process pending events */
        if (nevents > 0 && noutputs == 0 && error == 0) {
-
+               struct _kevent *cont_args;
                /* store the continuation/completion data in the uthread */
-               ut = (uthread_t)get_bsdthread_info(current_thread());
-               cont_args = &ut->uu_kevent.ss_kevent;
+               ut = (uthread_t)get_bsdthread_info(thread);
+               cont_args = &ut->uu_save.uus_kevent;
                cont_args->fp = fp;
                cont_args->fd = fd;
                cont_args->retval = retval;
@@ -2373,12 +4026,17 @@ kevent_internal(struct proc *p,
                cont_args->eventcount = nevents;
                cont_args->eventout = noutputs;
                cont_args->data_available = data_available;
-               cont_args->process_data.fp_fd = fd;
+               cont_args->process_data.fp_fd = (int)id;
                cont_args->process_data.fp_flags = flags;
                cont_args->process_data.fp_data_out = data_out;
                cont_args->process_data.fp_data_size = data_size;
                cont_args->process_data.fp_data_resid = data_size;
 
+               /*
+                * kqworkloop_end_processing() will happen at the end of kqueue_scan()
+                */
+               needs_end_processing = false;
+
                error = kqueue_scan(kq, kevent_callback,
                                    continuation, cont_args,
                                    &cont_args->process_data,
@@ -2395,6 +4053,18 @@ kevent_internal(struct proc *p,
                }
        }
 
+out:
+       if (__improbable(needs_end_processing)) {
+               /*
+                * If we didn't through kqworkloop_end_processing(),
+                * we need to do it here.
+                */
+               kqlock(kq);
+               kqworkloop_end_processing((struct kqworkloop *)kq, 0, 0);
+               kqunlock(kq);
+       }
+       kevent_put_kq(p, id, fp, kq);
+
        /* don't restart after signals... */
        if (error == ERESTART)
                error = EINTR;
@@ -2402,8 +4072,6 @@ kevent_internal(struct proc *p,
                error = 0;
        if (error == 0)
                *retval = noutputs;
-       if (fp != NULL)
-               fp_drop(p, fd, fp, 0);
        return (error);
 }
 
@@ -2416,7 +4084,7 @@ kevent_internal(struct proc *p,
  */
 static int
 kevent_callback(__unused struct kqueue *kq, struct kevent_internal_s *kevp,
-    void *data)
+               void *data)
 {
        struct _kevent *cont_args;
        int error;
@@ -2463,6 +4131,122 @@ kevent_description(struct kevent_internal_s *kevp, char *s, size_t n)
        return (s);
 }
 
+static int
+kevent_register_validate_priority(struct kqueue *kq, struct knote *kn,
+               struct kevent_internal_s *kev)
+{
+       /* We don't care about the priority of a disabled or deleted knote */
+       if (kev->flags & (EV_DISABLE | EV_DELETE)) {
+               return 0;
+       }
+
+       if (kq->kq_state & KQ_WORKLOOP) {
+               /*
+                * Workloops need valid priorities with a QOS (excluding manager) for
+                * any enabled knote.
+                *
+                * When it is pre-existing, just make sure it has a valid QoS as
+                * kevent_register() will not use the incoming priority (filters who do
+                * have the responsibility to validate it again, see filt_wltouch).
+                *
+                * If the knote is being made, validate the incoming priority.
+                */
+               if (!_pthread_priority_thread_qos(kn ? kn->kn_qos : kev->qos)) {
+                       return ERANGE;
+               }
+       }
+
+       return 0;
+}
+
+/*
+ * Prepare a filter for waiting after register.
+ *
+ * The f_post_register_wait hook will be called later by kevent_register()
+ * and should call kevent_register_wait_block()
+ */
+static int
+kevent_register_wait_prepare(struct knote *kn, struct kevent_internal_s *kev)
+{
+       thread_t thread = current_thread();
+       struct uthread *uth = get_bsdthread_info(thread);
+
+       assert(knote_fops(kn)->f_extended_codes);
+
+       if (kn->kn_hook == NULL) {
+               thread_reference(thread);
+               kn->kn_hook = thread;
+       } else if (kn->kn_hook != thread) {
+               /*
+                * kn_hook may be set from a previous aborted wait
+                * However, it has to be from the same thread.
+                */
+               kev->flags |= EV_ERROR;
+               kev->data = EXDEV;
+               return 0;
+       }
+
+       uth->uu_save.uus_kevent_register.knote = kn;
+       return FILTER_REGISTER_WAIT;
+}
+
+/*
+ * Cleanup a kevent_register_wait_prepare() effect for threads that have been
+ * aborted instead of properly woken up with thread_wakeup_thread().
+ */
+static void
+kevent_register_wait_cleanup(struct knote *kn)
+{
+       thread_t thread = kn->kn_hook;
+       kn->kn_hook = NULL;
+       thread_deallocate(thread);
+}
+
+/*
+ * Must be called at the end of a f_post_register_wait call from a filter.
+ */
+static void
+kevent_register_wait_block(struct turnstile *ts, thread_t thread,
+               struct knote_lock_ctx *knlc, thread_continue_t cont,
+               struct _kevent_register *cont_args)
+{
+       knote_unlock(cont_args->kq, cont_args->knote, knlc, KNOTE_KQ_UNLOCK);
+       turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_NOT_HELD);
+       cont_args->handoff_thread = thread;
+       thread_handoff_parameter(thread, cont, cont_args);
+}
+
+/*
+ * Called by Filters using a f_post_register_wait to return from their wait.
+ */
+static void
+kevent_register_wait_return(struct _kevent_register *cont_args)
+{
+       struct kqueue *kq = cont_args->kq;
+       proc_t p = kq->kq_p;
+       struct kevent_internal_s *kev = &cont_args->kev;
+       int error = 0;
+
+       if (cont_args->handoff_thread) {
+               thread_deallocate(cont_args->handoff_thread);
+       }
+
+       if (kev->flags & (EV_ERROR|EV_RECEIPT)) {
+               if ((kev->flags & EV_ERROR) == 0) {
+                       kev->flags |= EV_ERROR;
+                       kev->data = 0;
+               }
+               error = kevent_copyout(kev, &cont_args->ueventlist, p, cont_args->flags);
+               if (error == 0) cont_args->eventout++;
+       }
+
+       kevent_put_kq(p, cont_args->fd, cont_args->fp, kq);
+       if (error == 0) {
+               *cont_args->retval = cont_args->eventout;
+       }
+       unix_syscall_return(error);
+}
+
 /*
  * kevent_register - add a new event to a kqueue
  *
@@ -2477,15 +4261,15 @@ kevent_description(struct kevent_internal_s *kevp, char *s, size_t n)
  *     caller holds a reference on the kqueue
  */
 
-void
+int
 kevent_register(struct kqueue *kq, struct kevent_internal_s *kev,
-    __unused struct proc *ctxp)
+               struct knote_lock_ctx *knlc)
 {
        struct proc *p = kq->kq_p;
-       struct filterops *fops;
+       const struct filterops *fops;
        struct knote *kn = NULL;
-       int result = 0;
-       int error = 0;
+       int result = 0, error = 0;
+       unsigned short kev_flags = kev->flags;
 
        if (kev->filter < 0) {
                if (kev->filter + EVFILT_SYSCOUNT < 0) {
@@ -2500,7 +4284,7 @@ kevent_register(struct kqueue *kq, struct kevent_internal_s *kev,
 
        /* restrict EV_VANISHED to adding udata-specific dispatch kevents */
        if ((kev->flags & EV_VANISHED) &&
-           (kev->flags & (EV_ADD | EV_DISPATCH2)) != (EV_ADD | EV_DISPATCH2)) {
+                       (kev->flags & (EV_ADD | EV_DISPATCH2)) != (EV_ADD | EV_DISPATCH2)) {
                error = EINVAL;
                goto out;
        }
@@ -2511,256 +4295,273 @@ kevent_register(struct kqueue *kq, struct kevent_internal_s *kev,
        if (kev->flags & EV_DISABLE)
                kev->flags &= ~EV_ENABLE;
 
-restart:
-
-       proc_fdlock(p);
+       if (kq->kq_state & KQ_WORKLOOP) {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_REGISTER),
+                             ((struct kqworkloop *)kq)->kqwl_dynamicid,
+                             kev->udata, kev->flags, kev->filter);
+       } else if (kq->kq_state & KQ_WORKQ) {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWQ_REGISTER),
+                             0, kev->udata, kev->flags, kev->filter);
+       } else {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQ_REGISTER),
+                             VM_KERNEL_UNSLIDE_OR_PERM(kq),
+                             kev->udata, kev->flags, kev->filter);
+       }
 
+restart:
        /* find the matching knote from the fd tables/hashes */
-       kn = knote_fdfind(kq, kev, p);
-
-       if (kn == NULL) {
-               if (kev->flags & EV_ADD) {
-                       struct fileproc *fp = NULL;
-
-                       /* grab a file reference for the new knote */
-                       if (fops->f_isfd) {
-                               if ((error = fp_lookup(p, kev->ident, &fp, 1)) != 0) {
-                                       proc_fdunlock(p);
-                                       goto out;
-                               }
-                       }
-
-                       kn = knote_alloc();
-                       if (kn == NULL) {
-                               proc_fdunlock(p);
-                               error = ENOMEM;
-                               if (fp != NULL)
-                                       fp_drop(p, kev->ident, fp, 0);
-                               goto out;
-                       }
-
-                       kn->kn_fp = fp;
-                       knote_set_kq(kn,kq);
-                       kn->kn_filtid = ~kev->filter;
-                       kn->kn_inuse = 1;  /* for f_attach() */
-                       kn->kn_status = KN_ATTACHING | KN_ATTACHED;
-
-                       /* was vanish support requested */
-                       if (kev->flags & EV_VANISHED) {
-                               kev->flags &= ~EV_VANISHED;
-                               kn->kn_status |= KN_REQVANISH;
-                       }
+       kn = kq_find_knote_and_kq_lock(kq, kev, fops->f_isfd, p);
+       error = kevent_register_validate_priority(kq, kn, kev);
+       result = 0;
+       if (error) {
+               goto out;
+       }
 
-                       /* snapshot matching/dispatching protcol flags into knote */
-                       if (kev->flags & EV_DISPATCH)
-                               kn->kn_status |= KN_DISPATCH;
-                       if (kev->flags & EV_UDATA_SPECIFIC)
-                               kn->kn_status |= KN_UDATA_SPECIFIC;
+       if (kn == NULL && (kev->flags & EV_ADD) == 0) {
+               /*
+                * No knote found, EV_ADD wasn't specified
+                */
 
+               if ((kev_flags & EV_ADD) && (kev_flags & EV_DELETE) &&
+                               (kq->kq_state & KQ_WORKLOOP)) {
                        /*
-                        * copy the kevent state into knote
-                        * protocol is that fflags and data
-                        * are saved off, and cleared before
-                        * calling the attach routine.
+                        * For workloops, understand EV_ADD|EV_DELETE as a "soft" delete
+                        * that doesn't care about ENOENT, so just pretend the deletion
+                        * happened.
                         */
-                       kn->kn_kevent = *kev;
-                       kn->kn_sfflags = kev->fflags;
-                       kn->kn_sdata = kev->data;
-                       kn->kn_fflags = 0;
-                       kn->kn_data = 0;
-
-                       /* invoke pthread kext to convert kevent qos to thread qos */
-                       if (kq->kq_state & KQ_WORKQ) {
-                               kn->kn_qos = canonicalize_kevent_qos(kn->kn_qos);
-                               knote_set_qos_index(kn, qos_index_from_qos(kn->kn_qos, FALSE));
-                               knote_set_qos_override_index(kn, QOS_INDEX_KQFILE);
-                               assert(knote_get_qos_index(kn) < KQWQ_NQOS);
-                       } else {
-                               knote_set_qos_index(kn, QOS_INDEX_KQFILE);
-                               knote_set_qos_override_index(kn, QOS_INDEX_KQFILE);
-                       }
+               } else {
+                       error = ENOENT;
+               }
+               goto out;
 
-                       /* before anyone can find it */
-                       if (kev->flags & EV_DISABLE)
-                               knote_disable(kn);
+       } else if (kn == NULL) {
+               /*
+                * No knote found, need to attach a new one (attach)
+                */
 
-                       /* Add the knote for lookup thru the fd table */
-                       error = knote_fdadd(kn, p);
-                       proc_fdunlock(p);
+               struct fileproc *knote_fp = NULL;
 
-                       if (error) {
-                               knote_free(kn);
-                               if (fp != NULL)
-                                       fp_drop(p, kev->ident, fp, 0);
+               /* grab a file reference for the new knote */
+               if (fops->f_isfd) {
+                       if ((error = fp_lookup(p, kev->ident, &knote_fp, 0)) != 0) {
                                goto out;
                        }
+               }
 
-                       /* fp reference count now applies to knote */
-
-                       /* call filter attach routine */
-                       result = fops->f_attach(kn);
+               kn = knote_alloc();
+               if (kn == NULL) {
+                       error = ENOMEM;
+                       if (knote_fp != NULL)
+                               fp_drop(p, kev->ident, knote_fp, 0);
+                       goto out;
+               }
 
-                       /*
-                        * Trade knote use count for kq lock.
-                        * Cannot be dropped because we held
-                        * KN_ATTACHING throughout.
-                        */
-                       knoteuse2kqlock(kq, kn, 1);
+               kn->kn_fp = knote_fp;
+               kn->kn_kq_packed = (intptr_t)(struct kqueue *)kq;
+               kqueue_retain(kq); /* retain a kq ref */
+               kn->kn_filtid = ~kev->filter;
+               kn->kn_status = KN_ATTACHING | KN_ATTACHED;
 
-                       if (kn->kn_flags & EV_ERROR) {
-                               /*
-                                * Failed to attach correctly, so drop.
-                                * All other possible users/droppers
-                                * have deferred to us.  Save the error
-                                * to return to our caller.
-                                */
-                               kn->kn_status &= ~KN_ATTACHED;
-                               kn->kn_status |= KN_DROPPING;
-                               error = kn->kn_data;
-                               kqunlock(kq);
-                               knote_drop(kn, p);
-                               goto out;
-                       }
+               /* was vanish support requested */
+               if (kev->flags & EV_VANISHED) {
+                       kev->flags &= ~EV_VANISHED;
+                       kn->kn_status |= KN_REQVANISH;
+               }
 
-                       /* end "attaching" phase - now just attached */
-                       kn->kn_status &= ~KN_ATTACHING;
+               /* snapshot matching/dispatching protcol flags into knote */
+               if (kev->flags & EV_DISPATCH)
+                       kn->kn_status |= KN_DISPATCH;
+               if (kev->flags & EV_UDATA_SPECIFIC)
+                       kn->kn_status |= KN_UDATA_SPECIFIC;
+               if (kev->flags & EV_DISABLE)
+                       kn->kn_status |= KN_DISABLED;
 
-                       if (kn->kn_status & KN_DROPPING) {
-                               /*
-                                * Attach succeeded, but someone else
-                                * deferred their drop - now we have
-                                * to do it for them.
-                                */
-                               kqunlock(kq);
-                               knote_drop(kn, p);
-                               goto out;
-                       }
+               /*
+                * copy the kevent state into knote
+                * protocol is that fflags and data
+                * are saved off, and cleared before
+                * calling the attach routine.
+                */
+               kn->kn_kevent = *kev;
+               kn->kn_sfflags = kev->fflags;
+               kn->kn_sdata = kev->data;
+               kn->kn_fflags = 0;
+               kn->kn_data = 0;
+               knote_reset_priority(kn, kev->qos);
 
-                       /*
-                        * If the attach routine indicated that an
-                        * event is already fired, activate the knote.
-                        */
-                       if (result)
-                               knote_activate(kn);
+               /* Add the knote for lookup thru the fd table */
+               error = kq_add_knote(kq, kn, knlc, p);
+               if (error) {
+                       (void)kqueue_release(kq, KQUEUE_CANT_BE_LAST_REF);
+                       knote_free(kn);
+                       if (knote_fp != NULL)
+                               fp_drop(p, kev->ident, knote_fp, 0);
 
-               } else {
-                       proc_fdunlock(p);
-                       error = ENOENT;
+                       if (error == ERESTART) {
+                               goto restart;
+                       }
                        goto out;
                }
 
-       } else {
-               /* existing knote - get kqueue lock */
-               kqlock(kq);
-               proc_fdunlock(p);
+               /* fp reference count now applies to knote */
 
-               if ((kn->kn_status & (KN_DROPPING | KN_ATTACHING)) != 0) {
-                       /*
-                        * The knote is not in a stable state, wait for that
-                        * transition to complete and then redrive the lookup.
-                        */
-                       kn->kn_status |= KN_USEWAIT;
-                       waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
-                                           CAST_EVENT64_T(&kn->kn_status),
-                                           THREAD_UNINT, TIMEOUT_WAIT_FOREVER);
-                       kqunlock(kq);
-                       thread_block(THREAD_CONTINUE_NULL);
-                       goto restart;
+               /*
+                * we can't use filter_call() because f_attach can change the filter ops
+                * for a filter that supports f_extended_codes, so we need to reload
+                * knote_fops() and not use `fops`.
+                */
+               result = fops->f_attach(kn, kev);
+               if (result && !knote_fops(kn)->f_extended_codes) {
+                       result = FILTER_ACTIVE;
                }
 
-               if (kev->flags & EV_DELETE) {
+               kqlock(kq);
 
+               if (kn->kn_flags & EV_ERROR) {
                        /*
-                        * If attempting to delete a disabled dispatch2 knote,
-                        * we must wait for the knote to be re-enabled (unless
-                        * it is being re-enabled atomically here).
+                        * Failed to attach correctly, so drop.
                         */
-                       if ((kev->flags & EV_ENABLE) == 0 &&
-                           (kn->kn_status & (KN_DISPATCH2 | KN_DISABLED)) ==
-                                            (KN_DISPATCH2 | KN_DISABLED)) {
-                               kn->kn_status |= KN_DEFERDELETE;
-                               kqunlock(kq);
-                               error = EINPROGRESS;
-                       } else if (kqlock2knotedrop(kq, kn)) {
-                               knote_drop(kn, p);
-                       } else {
-                               /*
-                                * The kqueue is unlocked, it's not being
-                                * dropped, and kqlock2knotedrop returned 0:
-                                * this means that someone stole the drop of
-                                * the knote from us.
-                                */
-                               error = EINPROGRESS;
-                       }
+                       kn->kn_status &= ~(KN_ATTACHED | KN_ATTACHING);
+                       error = kn->kn_data;
+                       knote_drop(kq, kn, knlc);
+                       result = 0;
                        goto out;
                }
 
                /*
-                * If we are re-enabling a deferred-delete knote,
-                * just enable it now and avoid calling the
-                * filter touch routine (it has delivered its
-                * last event already).
+                * end "attaching" phase - now just attached
+                *
+                * Mark the thread request overcommit, if appropos
+                *
+                * If the attach routine indicated that an
+                * event is already fired, activate the knote.
                 */
-               if ((kev->flags & EV_ENABLE) &&
-                   (kn->kn_status & KN_DEFERDELETE)) {
-                       assert(kn->kn_status & KN_DISABLED);
+               kn->kn_status &= ~KN_ATTACHING;
+               knote_set_qos_overcommit(kn);
+
+               if (result & FILTER_ACTIVE) {
+                       if (result & FILTER_ADJUST_EVENT_QOS_BIT)
+                               knote_adjust_qos(kq, kn, result);
                        knote_activate(kn);
-                       knote_enable(kn);
-                       kqunlock(kq);
-                       goto out;
                }
 
+       } else if (!knote_lock(kq, kn, knlc, KNOTE_KQ_LOCK_ON_SUCCESS)) {
+
                /*
-                * If we are disabling, do it before unlocking and
-                * calling the touch routine (so no processing can
-                * see the new kevent state before the disable is
-                * applied).
+                * The knote was dropped while we were waiting for the lock,
+                * we need to re-evaluate entirely
                 */
-               if (kev->flags & EV_DISABLE)
-                       knote_disable(kn);
 
+               goto restart;
+
+       } else if (kev->flags & EV_DELETE) {
                /*
-                * Convert the kqlock to a use reference on the
-                * knote so we can call the filter touch routine.
+                * Deletion of a knote (drop)
+                *
+                * If the filter wants to filter drop events, let it do so.
+                *
+                * defer-delete: when trying to delete a disabled EV_DISPATCH2 knote,
+                * we must wait for the knote to be re-enabled (unless it is being
+                * re-enabled atomically here).
                 */
-               if (kqlock2knoteuse(kq, kn)) {
 
-                       /*
-                        * Call touch routine to notify filter of changes
-                        * in filter values (and to re-determine if any
-                        * events are fired).
-                        */
-                       result = knote_fops(kn)->f_touch(kn, kev);
+               if (knote_fops(kn)->f_allow_drop) {
+                       bool drop;
 
-                       /* Get the kq lock back (don't defer droppers). */
-                       if (!knoteuse2kqlock(kq, kn, 0)) {
-                               kqunlock(kq);
-                               goto out;
-                       }
+                       kqunlock(kq);
+                       drop = knote_fops(kn)->f_allow_drop(kn, kev);
+                       kqlock(kq);
 
-                       /* Activate it if the touch routine said to */
-                       if (result)
-                               knote_activate(kn);
+                       if (!drop) goto out_unlock;
                }
 
-               /* Enable the knote if called for */
-               if (kev->flags & EV_ENABLE)
-                       knote_enable(kn);
+               if ((kev->flags & EV_ENABLE) == 0 &&
+                               (kn->kn_status & (KN_DISPATCH2 | KN_DISABLED)) ==
+                               (KN_DISPATCH2 | KN_DISABLED)) {
+                       kn->kn_status |= KN_DEFERDELETE;
+                       error = EINPROGRESS;
+                       goto out_unlock;
+               }
+
+               knote_drop(kq, kn, knlc);
+               goto out;
+
+       } else {
+               /*
+                * Regular update of a knote (touch)
+                *
+                * Call touch routine to notify filter of changes in filter values
+                * (and to re-determine if any events are fired).
+                *
+                * If the knote is in defer-delete, avoid calling the filter touch
+                * routine (it has delivered its last event already).
+                *
+                * If the touch routine had no failure,
+                * apply the requested side effects to the knote.
+                */
+
+               if (kn->kn_status & (KN_DEFERDELETE | KN_VANISHED)) {
+                       if (kev->flags & EV_ENABLE) {
+                               result = FILTER_ACTIVE;
+                       }
+               } else {
+                       kqunlock(kq);
+                       result = filter_call(knote_fops(kn), f_touch(kn, kev));
+                       kqlock(kq);
+               }
 
+               if (kev->flags & EV_ERROR) {
+                       result = 0;
+               } else {
+                       /* accept new kevent state */
+                       if ((kn->kn_status & KN_UDATA_SPECIFIC) == 0)
+                               kn->kn_udata = kev->udata;
+                       if (kev->flags & EV_DISABLE)
+                               knote_disable(kn);
+                       if (result & (FILTER_UPDATE_REQ_QOS | FILTER_ADJUST_EVENT_QOS_BIT))
+                               knote_dequeue(kn);
+                       if ((result & FILTER_UPDATE_REQ_QOS) &&
+                                       kev->qos && kev->qos != kn->kn_qos) {
+                               knote_reset_priority(kn, kev->qos);
+                       }
+                       if (result & FILTER_ACTIVE) {
+                               thread_qos_t qos;
+                               if (result & FILTER_ADJUST_EVENT_QOS_BIT) {
+                                       if (knote_should_apply_qos_override(kq, kn, result, &qos)) {
+                                               knote_apply_qos_override(kn, qos);
+                                       }
+                               }
+                               knote_activate(kn);
+                       }
+                       if (result & (FILTER_UPDATE_REQ_QOS | FILTER_ADJUST_EVENT_QOS_BIT)) {
+                               if (knote_enqueue(kn) && (kn->kn_status & KN_ACTIVE)) {
+                                       knote_wakeup(kn);
+                               }
+                       }
+                       if (kev->flags & EV_ENABLE)
+                               knote_enable(kn);
+               }
        }
 
-       /* still have kqlock held and knote is valid */
-       kqunlock(kq);
+out_unlock:
+       if ((result & FILTER_REGISTER_WAIT) == 0) {
+               /*
+                * When the filter asked for a post-register wait,
+                * we leave the knote and kqueue locked for kevent_register()
+                * to call the filter's f_post_register_wait hook.
+                */
+               knote_unlock(kq, kn, knlc, KNOTE_KQ_UNLOCK);
+       }
 
- out:
+out:
        /* output local errors through the kevent */
        if (error) {
                kev->flags |= EV_ERROR;
                kev->data = error;
        }
+       return result;
 }
 
-
 /*
  * knote_process - process a triggered event
  *
@@ -2782,16 +4583,17 @@ restart:
  *     kqueue locked on entry and exit - but may be dropped
  */
 static int
-knote_process(struct knote *kn,        
+knote_process(struct knote *kn,
        kevent_callback_t callback,
        void *callback_data,
-       struct filt_process_s *process_data,
-       struct proc *p)
+       struct filt_process_s *process_data)
 {
        struct kevent_internal_s kev;
        struct kqueue *kq = knote_get_kq(kn);
-       int result = 0;
+       KNOTE_LOCK_CTX(knlc);
+       int result = FILTER_ACTIVE;
        int error = 0;
+       bool drop = false;
 
        bzero(&kev, sizeof(kev));
 
@@ -2803,106 +4605,108 @@ knote_process(struct knote *kn,
        assert(kn->kn_status & (KN_ACTIVE|KN_STAYACTIVE));
        assert(!(kn->kn_status & (KN_DISABLED|KN_SUPPRESSED|KN_DROPPING)));
 
+       if (kq->kq_state & KQ_WORKLOOP) {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS),
+                             ((struct kqworkloop *)kq)->kqwl_dynamicid,
+                             kn->kn_udata, kn->kn_status | (kn->kn_id << 32),
+                             kn->kn_filtid);
+       } else if (kq->kq_state & KQ_WORKQ) {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWQ_PROCESS),
+                             0, kn->kn_udata, kn->kn_status | (kn->kn_id << 32),
+                             kn->kn_filtid);
+       } else {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQ_PROCESS),
+                             VM_KERNEL_UNSLIDE_OR_PERM(kq), kn->kn_udata,
+                             kn->kn_status | (kn->kn_id << 32), kn->kn_filtid);
+       }
+
+       if ((kn->kn_status & KN_DROPPING) ||
+                       !knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ALWAYS)) {
+               /*
+                * When the knote is dropping or has dropped,
+                * then there's nothing we want to process.
+                */
+               return EJUSTRETURN;
+       }
+
        /*
         * For deferred-drop or vanished events, we just create a fake
         * event to acknowledge end-of-life.  Otherwise, we call the
         * filter's process routine to snapshot the kevent state under
         * the filter's locking protocol.
+        *
+        * suppress knotes to avoid returning the same event multiple times in
+        * a single call.
         */
+       knote_suppress(kn);
+
        if (kn->kn_status & (KN_DEFERDELETE | KN_VANISHED)) {
                /* create fake event */
                kev.filter = kn->kn_filter;
                kev.ident = kn->kn_id;
-               kev.qos = kn->kn_qos;
-               kev.flags = (kn->kn_status & KN_DEFERDELETE) ? 
-                           EV_DELETE : EV_VANISHED;
+               kev.flags = (kn->kn_status & KN_DEFERDELETE) ? EV_DELETE : EV_VANISHED;
                kev.flags |= (EV_DISPATCH2 | EV_ONESHOT);
                kev.udata = kn->kn_udata;
-               result = 1;
-
-               knote_suppress(kn);
        } else {
-
                /* deactivate - so new activations indicate a wakeup */
                knote_deactivate(kn);
 
-               /* suppress knotes to avoid returning the same event multiple times in a single call. */
-               knote_suppress(kn);
-
-               /* convert lock to a knote use reference */
-               if (!kqlock2knoteuse(kq, kn))
-                       panic("dropping knote found on queue\n");
-
-               /* call out to the filter to process with just a ref */
-               result = knote_fops(kn)->f_process(kn, process_data, &kev);
+               kqunlock(kq);
+               result = filter_call(knote_fops(kn), f_process(kn, process_data, &kev));
+               kqlock(kq);
+       }
 
-               /*
-                * convert our reference back to a lock. accept drop
-                * responsibility from others if we've committed to
-                * delivering event data.
-                */
-               if (!knoteuse2kqlock(kq, kn, result)) {
-                       /* knote dropped */
-                       kn = NULL;
+       /*
+        * Determine how to dispatch the knote for future event handling.
+        * not-fired: just return (do not callout, leave deactivated).
+        * One-shot:  If dispatch2, enter deferred-delete mode (unless this is
+        *            is the deferred delete event delivery itself).  Otherwise,
+        *            drop it.
+        * Dispatch:  don't clear state, just mark it disabled.
+        * Cleared:   just leave it deactivated.
+        * Others:    re-activate as there may be more events to handle.
+        *            This will not wake up more handlers right now, but
+        *            at the completion of handling events it may trigger
+        *            more handler threads (TODO: optimize based on more than
+        *            just this one event being detected by the filter).
+        */
+       if ((result & FILTER_ACTIVE) == 0) {
+               if ((kn->kn_status & (KN_ACTIVE | KN_STAYACTIVE)) == 0) {
+                       /*
+                        * Stay active knotes should not be unsuppressed or we'd create an
+                        * infinite loop.
+                        *
+                        * Some knotes (like EVFILT_WORKLOOP) can be reactivated from
+                        * within f_process() but that doesn't necessarily make them
+                        * ready to process, so we should leave them be.
+                        *
+                        * For other knotes, since we will not return an event,
+                        * there's no point keeping the knote suppressed.
+                        */
+                       knote_unsuppress(kn);
                }
+               knote_unlock(kq, kn, &knlc, KNOTE_KQ_LOCK_ALWAYS);
+               return EJUSTRETURN;
        }
 
-       if (kn != NULL) {
-               /*
-                * Determine how to dispatch the knote for future event handling.
-                * not-fired: just return (do not callout, leave deactivated).
-                * One-shot:  If dispatch2, enter deferred-delete mode (unless this is
-                *            is the deferred delete event delivery itself).  Otherwise,
-                *            drop it.
-                * stolendrop:We took responsibility for someone else's drop attempt.
-                *            treat this just like one-shot and prepare to turn it back
-                *            into a deferred delete if required.
-                * Dispatch:  don't clear state, just mark it disabled.
-                * Cleared:   just leave it deactivated.
-                * Others:    re-activate as there may be more events to handle.
-                *            This will not wake up more handlers right now, but
-                *            at the completion of handling events it may trigger
-                *            more handler threads (TODO: optimize based on more than
-                *            just this one event being detected by the filter).
-                */
-
-               if (result == 0)
-                       return (EJUSTRETURN);
+       if (result & FILTER_ADJUST_EVENT_QOS_BIT)
+               knote_adjust_qos(kq, kn, result);
+       kev.qos = _pthread_priority_combine(kn->kn_qos, kn->kn_qos_override);
 
-               if ((kev.flags & EV_ONESHOT) || (kn->kn_status & KN_STOLENDROP)) {
-                       if ((kn->kn_status & (KN_DISPATCH2 | KN_DEFERDELETE)) == KN_DISPATCH2) {
-                               /* defer dropping non-delete oneshot dispatch2 events */
-                               kn->kn_status |= KN_DEFERDELETE;
-                               knote_disable(kn);
-
-                               /* if we took over another's drop clear those flags here */
-                               if (kn->kn_status & KN_STOLENDROP) {
-                                       assert(kn->kn_status & KN_DROPPING);
-                                       /*
-                                        * the knote will be dropped when the
-                                        * deferred deletion occurs
-                                        */
-                                       kn->kn_status &= ~(KN_DROPPING|KN_STOLENDROP);
-                               }
-                       } else if (kn->kn_status & KN_STOLENDROP) {
-                               /* We now own the drop of the knote. */
-                               assert(kn->kn_status & KN_DROPPING);
-                               knote_unsuppress(kn);
-                               kqunlock(kq);
-                               knote_drop(kn, p);
-                               kqlock(kq);
-                       } else if (kqlock2knotedrop(kq, kn)) {
-                               /* just EV_ONESHOT, _not_ DISPATCH2 */
-                               knote_drop(kn, p);
-                               kqlock(kq);
-                       }
-               } else if (kn->kn_status & KN_DISPATCH) {
-                       /* disable all dispatch knotes */
+       if (kev.flags & EV_ONESHOT) {
+               if ((kn->kn_status & (KN_DISPATCH2 | KN_DEFERDELETE)) == KN_DISPATCH2) {
+                       /* defer dropping non-delete oneshot dispatch2 events */
+                       kn->kn_status |= KN_DEFERDELETE;
                        knote_disable(kn);
-               } else if ((kev.flags & EV_CLEAR) == 0) {
-                       /* re-activate in case there are more events */
-                       knote_activate(kn);
+               } else {
+                       drop = true;
                }
+       } else if (kn->kn_status & KN_DISPATCH) {
+               /* disable all dispatch knotes */
+               knote_disable(kn);
+       } else if ((kev.flags & EV_CLEAR) == 0) {
+               /* re-activate in case there are more events */
+               knote_activate(kn);
        }
 
        /*
@@ -2910,14 +4714,113 @@ knote_process(struct knote *kn,
         * If we have to detach and drop the knote, do
         * it while we have the kq unlocked.
         */
-       if (result) {
-               kqunlock(kq);
-               error = (callback)(kq, &kev, callback_data);
-               kqlock(kq);
+       if (drop) {
+               knote_drop(kq, kn, &knlc);
+       } else {
+               knote_unlock(kq, kn, &knlc, KNOTE_KQ_UNLOCK);
        }
-       return (error);
+
+       if (kev.flags & EV_VANISHED) {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KNOTE_VANISHED),
+                             kev.ident, kn->kn_udata, kn->kn_status | (kn->kn_id << 32),
+                             kn->kn_filtid);
+       }
+
+       error = (callback)(kq, &kev, callback_data);
+       kqlock(kq);
+       return error;
 }
 
+/*
+ * Returns -1 if the kqueue was unbound and processing should not happen
+ */
+#define KQWQAE_BEGIN_PROCESSING 1
+#define KQWQAE_END_PROCESSING   2
+#define KQWQAE_UNBIND           3
+static int
+kqworkq_acknowledge_events(struct kqworkq *kqwq, struct kqrequest *kqr,
+               int kevent_flags, int kqwqae_op)
+{
+       thread_qos_t old_override = THREAD_QOS_UNSPECIFIED;
+       thread_t thread = kqr->kqr_thread;
+       struct knote *kn;
+       int rc = 0;
+       bool seen_stayactive = false, unbind;
+
+       kqlock_held(&kqwq->kqwq_kqueue);
+
+       if (!TAILQ_EMPTY(&kqr->kqr_suppressed)) {
+               /*
+                * Return suppressed knotes to their original state.
+                * For workq kqueues, suppressed ones that are still
+                * truly active (not just forced into the queue) will
+                * set flags we check below to see if anything got
+                * woken up.
+                */
+               while ((kn = TAILQ_FIRST(&kqr->kqr_suppressed)) != NULL) {
+                       assert(kn->kn_status & KN_SUPPRESSED);
+                       knote_unsuppress(kn);
+                       if (kn->kn_status & KN_STAYACTIVE) {
+                               seen_stayactive = true;
+                       }
+               }
+       }
+
+       kq_req_lock(kqwq);
+
+#if DEBUG || DEVELOPMENT
+       thread_t self = current_thread();
+       struct uthread *ut = get_bsdthread_info(self);
+
+       assert(kqr->kqr_state & KQR_THREQUESTED);
+       assert(kqr->kqr_thread == self);
+       assert(ut->uu_kqr_bound == kqr);
+#endif // DEBUG || DEVELOPMENT
+
+       if (kqwqae_op == KQWQAE_UNBIND) {
+               unbind = true;
+       } else if ((kevent_flags & KEVENT_FLAG_PARKING) == 0) {
+               unbind = false;
+       } else if (kqwqae_op == KQWQAE_BEGIN_PROCESSING && seen_stayactive) {
+               /*
+                * When we unsuppress stayactive knotes, for the kind that are hooked
+                * through select, we need to process once before we can assert there's
+                * no event pending. Hence we can't unbind during BEGIN PROCESSING.
+                */
+               unbind = false;
+       } else {
+               unbind = ((kqr->kqr_state & KQR_WAKEUP) == 0);
+       }
+       if (unbind) {
+               old_override = kqworkq_unbind_locked(kqwq, kqr, thread);
+               rc = -1;
+               /*
+                * request a new thread if we didn't process the whole queue or real events
+                * have happened (not just putting stay-active events back).
+                */
+               if (kqr->kqr_state & KQR_WAKEUP) {
+                       kqueue_threadreq_initiate(&kqwq->kqwq_kqueue, kqr,
+                                       kqr->kqr_qos_index, 0);
+               }
+       }
+
+       if (rc == 0) {
+               /*
+                * Reset wakeup bit to notice events firing while we are processing,
+                * as we cannot rely on the bucket queue emptiness because of stay
+                * active knotes.
+                */
+               kqr->kqr_state &= ~KQR_WAKEUP;
+       }
+
+       kq_req_unlock(kqwq);
+
+       if (old_override) {
+               thread_drop_ipc_override(thread);
+       }
+
+       return rc;
+}
 
 /*
  * Return 0 to indicate that processing should proceed,
@@ -2927,57 +4830,165 @@ knote_process(struct knote *kn,
  * but may drop lock temporarily.
  */
 static int
-kqworkq_begin_processing(struct kqworkq *kqwq, kq_index_t qos_index, int flags)
+kqworkq_begin_processing(struct kqworkq *kqwq, struct kqrequest *kqr,
+               int kevent_flags)
 {
-       struct kqrequest *kqr;
-       thread_t self = current_thread();
-       __assert_only struct uthread *ut = get_bsdthread_info(self);
-       thread_t thread;
+       int rc = 0;
 
-       assert(kqwq->kqwq_state & KQ_WORKQ);
-       assert(qos_index < KQWQ_NQOS);
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWQ_PROCESS_BEGIN) | DBG_FUNC_START,
+                       0, kqr->kqr_qos_index);
 
-       kqwq_req_lock(kqwq);
-       kqr = kqworkq_get_request(kqwq, qos_index);
+       rc = kqworkq_acknowledge_events(kqwq, kqr, kevent_flags,
+                       KQWQAE_BEGIN_PROCESSING);
+
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWQ_PROCESS_BEGIN) | DBG_FUNC_END,
+                       thread_tid(kqr->kqr_thread), kqr->kqr_state);
 
-       thread = kqr->kqr_thread;
+       return rc;
+}
+
+static inline bool
+kqworkloop_is_processing_on_current_thread(struct kqworkloop *kqwl)
+{
+       struct kqueue *kq = &kqwl->kqwl_kqueue;
 
-       /* manager skips buckets that haven't ask for its help */
-       if (flags & KEVENT_FLAG_WORKQ_MANAGER) {
+       kqlock_held(kq);
 
-               /* If nothing for manager to do, just return */
-               if ((kqr->kqr_state & KQWQ_THMANAGER) == 0) {
-                       assert(kqr->kqr_thread != self);
-                       kqwq_req_unlock(kqwq);
-                       return -1;
+       if (kq->kq_state & KQ_PROCESSING) {
+               /*
+                * KQ_PROCESSING is unset with the kqlock held, and the kqr thread is
+                * never modified while KQ_PROCESSING is set, meaning that peeking at
+                * its value is safe from this context.
+                */
+               return kqwl->kqwl_request.kqr_thread == current_thread();
+       }
+       return false;
+}
+
+static thread_qos_t
+kqworkloop_acknowledge_events(struct kqworkloop *kqwl)
+{
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       kq_index_t qos = THREAD_QOS_UNSPECIFIED;
+       struct knote *kn, *tmp;
+
+       kqlock_held(&kqwl->kqwl_kqueue);
+
+       TAILQ_FOREACH_SAFE(kn, &kqr->kqr_suppressed, kn_tqe, tmp) {
+               /*
+                * If a knote that can adjust QoS is disabled because of the automatic
+                * behavior of EV_DISPATCH, the knotes should stay suppressed so that
+                * further overrides keep pushing.
+                */
+               if (knote_fops(kn)->f_adjusts_qos && (kn->kn_status & KN_DISABLED) &&
+                               (kn->kn_status & (KN_STAYACTIVE | KN_DROPPING)) == 0 &&
+                               (kn->kn_flags & (EV_DISPATCH | EV_DISABLE)) == EV_DISPATCH) {
+                       qos = MAX(qos, knote_get_qos_override_index(kn));
+                       continue;
+               }
+               knote_unsuppress(kn);
+       }
+
+       return qos;
+}
+
+static int
+kqworkloop_begin_processing(struct kqworkloop *kqwl, unsigned int kevent_flags)
+{
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       struct kqueue *kq = &kqwl->kqwl_kqueue;
+       thread_qos_t old_override = THREAD_QOS_UNSPECIFIED, qos_override;
+       thread_t thread = kqr->kqr_thread;
+       int rc = 0, op = KQWL_UTQ_NONE;
+
+       kqlock_held(kq);
+
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS_BEGIN) | DBG_FUNC_START,
+                     kqwl->kqwl_dynamicid, 0, 0);
+
+       /* nobody else should still be processing */
+       assert((kq->kq_state & KQ_PROCESSING) == 0);
+
+       kq->kq_state |= KQ_PROCESSING;
+
+       if (!TAILQ_EMPTY(&kqr->kqr_suppressed)) {
+               op = KQWL_UTQ_RESET_WAKEUP_OVERRIDE;
+       }
+
+       if (kevent_flags & KEVENT_FLAG_PARKING) {
+               /*
+                * When "parking" we want to process events and if no events are found
+                * unbind.
+                *
+                * However, non overcommit threads sometimes park even when they have
+                * more work so that the pool can narrow.  For these, we need to unbind
+                * early, so that calling kqworkloop_update_threads_qos() can ask the
+                * workqueue subsystem whether the thread should park despite having
+                * pending events.
+                */
+               if (kqr->kqr_state & KQR_THOVERCOMMIT) {
+                       op = KQWL_UTQ_PARKING;
+               } else {
+                       op = KQWL_UTQ_UNBINDING;
                }
+       }
+       if (op == KQWL_UTQ_NONE) {
+               goto done;
+       }
+
+       qos_override = kqworkloop_acknowledge_events(kqwl);
 
-               /* bind manager thread from this time on */
-               kqworkq_bind_thread(kqwq, qos_index, self, flags);
+       kq_req_lock(kqwl);
+
+       if (op == KQWL_UTQ_UNBINDING) {
+               old_override = kqworkloop_unbind_locked(kqwl, thread);
+               (void)kqueue_release(kqwl, KQUEUE_CANT_BE_LAST_REF);
+       }
+       kqworkloop_update_threads_qos(kqwl, op, qos_override);
+       if (op == KQWL_UTQ_PARKING) {
+               if (!TAILQ_EMPTY(&kqwl->kqwl_queue[KQWL_BUCKET_STAYACTIVE])) {
+                       /*
+                        * We cannot trust KQR_WAKEUP when looking at stay active knotes.
+                        * We need to process once, and kqworkloop_end_processing will
+                        * handle the unbind.
+                        */
+               } else if ((kqr->kqr_state & KQR_WAKEUP) == 0 || kqwl->kqwl_owner) {
+                       old_override = kqworkloop_unbind_locked(kqwl, thread);
+                       (void)kqueue_release(kqwl, KQUEUE_CANT_BE_LAST_REF);
+                       rc = -1;
+               }
+       } else if (op == KQWL_UTQ_UNBINDING) {
+               if (kqr->kqr_thread == thread) {
+                       /*
+                        * The thread request fired again, passed the admission check and
+                        * got bound to the current thread again.
+                        */
+               } else {
+                       rc = -1;
+               }
+       }
 
+       if (rc == 0) {
+               /*
+                * Reset wakeup bit to notice stay active events firing while we are
+                * processing, as we cannot rely on the stayactive bucket emptiness.
+                */
+               kqr->kqr_wakeup_indexes &= ~KQWL_STAYACTIVE_FIRED_BIT;
        } else {
-               /* must have been bound by now */
-               assert(thread == self);
-               assert(ut->uu_kqueue_bound == qos_index);
-               assert((ut->uu_kqueue_flags & flags) == ut->uu_kqueue_flags);
+               kq->kq_state &= ~KQ_PROCESSING;
        }
 
-       /* nobody else should still be processing */
-       assert(kqr->kqr_state & KQWQ_THREQUESTED);
-       assert((kqr->kqr_state & KQWQ_PROCESSING) == 0);
-                  
-       /* anything left to process? */
-       if (kqueue_queue_empty(&kqwq->kqwq_kqueue, qos_index)) {
-               kqwq_req_unlock(kqwq);
-               return -1;
+       kq_req_unlock(kqwl);
+
+       if (old_override) {
+               thread_drop_ipc_override(thread);
        }
 
-       /* convert to processing mode */
-       /* reset workq triggers and thread requests - maybe processing */
-       kqr->kqr_state &= ~(KQWQ_HOOKCALLED | KQWQ_WAKEUP);
-       kqr->kqr_state |= KQWQ_PROCESSING;
-       kqwq_req_unlock(kqwq);
-       return 0;
+done:
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS_BEGIN) | DBG_FUNC_END,
+                     kqwl->kqwl_dynamicid, 0, 0);
+
+       return rc;
 }
 
 /*
@@ -2989,30 +5000,34 @@ kqworkq_begin_processing(struct kqworkq *kqwq, kq_index_t qos_index, int flags)
  * May block.
  */
 static int
-kqueue_begin_processing(struct kqueue *kq, kq_index_t qos_index, unsigned int flags)
+kqfile_begin_processing(struct kqueue *kq)
 {
        struct kqtailq *suppressq;
 
-       if (kq->kq_state & KQ_WORKQ)
-               return kqworkq_begin_processing((struct kqworkq *)kq, qos_index, flags);
+       kqlock_held(kq);
 
-       assert(qos_index == QOS_INDEX_KQFILE);
+       assert((kq->kq_state & (KQ_WORKQ | KQ_WORKLOOP)) == 0);
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_BEGIN) | DBG_FUNC_START,
+                     VM_KERNEL_UNSLIDE_OR_PERM(kq), 0);
 
        /* wait to become the exclusive processing thread */
        for (;;) {
-               if (kq->kq_state & KQ_DRAIN)
+               if (kq->kq_state & KQ_DRAIN) {
+                       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_BEGIN) | DBG_FUNC_END,
+                                     VM_KERNEL_UNSLIDE_OR_PERM(kq), 2);
                        return -1;
+               }
 
                if ((kq->kq_state & KQ_PROCESSING) == 0)
                        break;
 
                /* if someone else is processing the queue, wait */
                kq->kq_state |= KQ_PROCWAIT;
-               suppressq = kqueue_get_suppressed_queue(kq, qos_index);
+               suppressq = kqueue_get_suppressed_queue(kq, NULL);
                waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
-                                   CAST_EVENT64_T(suppressq),
-                                   THREAD_UNINT, TIMEOUT_WAIT_FOREVER);
-               
+                               CAST_EVENT64_T(suppressq), THREAD_UNINT | THREAD_WAIT_NOREPORT,
+                               TIMEOUT_WAIT_FOREVER);
+
                kqunlock(kq);
                thread_block(THREAD_CONTINUE_NULL);
                kqlock(kq);
@@ -3023,427 +5038,423 @@ kqueue_begin_processing(struct kqueue *kq, kq_index_t qos_index, unsigned int fl
        /* clear pre-posts and KQ_WAKEUP now, in case we bail early */
        waitq_set_clear_preposts(&kq->kq_wqs);
        kq->kq_state &= ~KQ_WAKEUP;
-                  
+
        /* anything left to process? */
-       if (kqueue_queue_empty(kq, qos_index))
+       if (kqueue_queue_empty(kq, QOS_INDEX_KQFILE)) {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_BEGIN) | DBG_FUNC_END,
+                             VM_KERNEL_UNSLIDE_OR_PERM(kq), 1);
                return -1;
+       }
 
        /* convert to processing mode */
        kq->kq_state |= KQ_PROCESSING;
 
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_BEGIN) | DBG_FUNC_END,
+                     VM_KERNEL_UNSLIDE_OR_PERM(kq));
+
        return 0;
 }
 
 /*
- *     kqworkq_end_processing - Complete the processing of a workq kqueue
- *
- *     We may have to request new threads.
- *     This can happen there are no waiting processing threads and:
- *     - there were active events we never got to (count > 0)
- *     - we pended waitq hook callouts during processing
- *     - we pended wakeups while processing (or unsuppressing)
+ * Try to end the processing, only called when a workq thread is attempting to
+ * park (KEVENT_FLAG_PARKING is set).
  *
- *     Called with kqueue lock held.
+ * When returning -1, the kqworkq is setup again so that it is ready to be
+ * processed.
  */
-static void
-kqworkq_end_processing(struct kqworkq *kqwq, kq_index_t qos_index, int flags)
+static int
+kqworkq_end_processing(struct kqworkq *kqwq, struct kqrequest *kqr,
+               int kevent_flags)
 {
-#pragma unused(flags)
+       if (!kqueue_queue_empty(&kqwq->kqwq_kqueue, kqr->kqr_qos_index)) {
+               /* remember we didn't process everything */
+               kq_req_lock(kqwq);
+               kqr->kqr_state |= KQR_WAKEUP;
+               kq_req_unlock(kqwq);
+       }
 
-       struct kqueue *kq = &kqwq->kqwq_kqueue;
-       struct kqtailq *suppressq = kqueue_get_suppressed_queue(kq, qos_index);
+       if (kevent_flags & KEVENT_FLAG_PARKING) {
+               /*
+                * if acknowledge events "succeeds" it means there are events,
+                * which is a failure condition for end_processing.
+                */
+               int rc = kqworkq_acknowledge_events(kqwq, kqr, kevent_flags,
+                               KQWQAE_END_PROCESSING);
+               if (rc == 0) {
+                       return -1;
+               }
+       }
 
-       thread_t self = current_thread();
-       __assert_only struct uthread *ut = get_bsdthread_info(self);
-       struct knote *kn;
-       struct kqrequest *kqr;
-       int queued_events;
-       uint16_t pended;
-       thread_t thread;
+       return 0;
+}
+
+/*
+ * Try to end the processing, only called when a workq thread is attempting to
+ * park (KEVENT_FLAG_PARKING is set).
+ *
+ * When returning -1, the kqworkq is setup again so that it is ready to be
+ * processed (as if kqworkloop_begin_processing had just been called).
+ *
+ * If successful and KEVENT_FLAG_PARKING was set in the kevent_flags,
+ * the kqworkloop is unbound from its servicer as a side effect.
+ */
+static int
+kqworkloop_end_processing(struct kqworkloop *kqwl, int flags, int kevent_flags)
+{
+       struct kqueue *kq = &kqwl->kqwl_kqueue;
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       thread_qos_t old_override = THREAD_QOS_UNSPECIFIED, qos_override;
+       thread_t thread = kqr->kqr_thread;
+       int rc = 0;
 
-       assert(kqwq->kqwq_state & KQ_WORKQ);
-       assert(qos_index < KQWQ_NQOS);
+       kqlock_held(kq);
 
-       /* leave early if we are not even processing */
-       kqwq_req_lock(kqwq);
-       kqr = kqworkq_get_request(kqwq, qos_index);
-       thread = kqr->kqr_thread;
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS_END) | DBG_FUNC_START,
+                       kqwl->kqwl_dynamicid, 0, 0);
 
-       if (flags & KEVENT_FLAG_WORKQ_MANAGER) {
-               assert(ut->uu_kqueue_bound == KQWQ_QOS_MANAGER);
-               assert(ut->uu_kqueue_flags & KEVENT_FLAG_WORKQ_MANAGER);
+       if (flags & KQ_PROCESSING) {
+               assert(kq->kq_state & KQ_PROCESSING);
 
-               /* if this bucket didn't need manager help, bail */
-               if ((kqr->kqr_state & KQWQ_THMANAGER) == 0) {
-                       assert(thread != self);
-                       kqwq_req_unlock(kqwq);
-                       return;
+               /*
+                * If we still have queued stayactive knotes, remember we didn't finish
+                * processing all of them.  This should be extremely rare and would
+                * require to have a lot of them registered and fired.
+                */
+               if (!TAILQ_EMPTY(&kqwl->kqwl_queue[KQWL_BUCKET_STAYACTIVE])) {
+                       kq_req_lock(kqwl);
+                       kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_UPDATE_WAKEUP_QOS,
+                                       KQWL_BUCKET_STAYACTIVE);
+                       kq_req_unlock(kqwl);
+               }
+
+               /*
+                * When KEVENT_FLAG_PARKING is set, we need to attempt an unbind while
+                * still under the lock.
+                *
+                * So we do everything kqworkloop_unbind() would do, but because we're
+                * inside kqueue_process(), if the workloop actually received events
+                * while our locks were dropped, we have the opportunity to fail the end
+                * processing and loop again.
+                *
+                * This avoids going through the process-wide workqueue lock hence
+                * scales better.
+                */
+               if (kevent_flags & KEVENT_FLAG_PARKING) {
+                       qos_override = kqworkloop_acknowledge_events(kqwl);
                }
+       }
 
-               assert(kqr->kqr_state & KQWQ_THREQUESTED);
+       kq_req_lock(kqwl);
 
-               /* unbound bucket - see if still needs servicing */
-               if (thread == THREAD_NULL) {
-                       assert((kqr->kqr_state & KQWQ_PROCESSING) == 0);
-                       assert(TAILQ_EMPTY(suppressq));
+       if (kevent_flags & KEVENT_FLAG_PARKING) {
+               kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_PARKING, qos_override);
+               if ((kqr->kqr_state & KQR_WAKEUP) && !kqwl->kqwl_owner) {
+                       /*
+                        * Reset wakeup bit to notice stay active events firing while we are
+                        * processing, as we cannot rely on the stayactive bucket emptiness.
+                        */
+                       kqr->kqr_wakeup_indexes &= ~KQWL_STAYACTIVE_FIRED_BIT;
+                       rc = -1;
                } else {
-                       assert(thread == self);
+                       old_override = kqworkloop_unbind_locked(kqwl, thread);
+                       (void)kqueue_release(kqwl, KQUEUE_CANT_BE_LAST_REF);
+                       kq->kq_state &= ~flags;
                }
-
        } else {
-               assert(thread == self);
-               assert(ut->uu_kqueue_bound == qos_index);
-               assert((ut->uu_kqueue_flags & KEVENT_FLAG_WORKQ_MANAGER) == 0);
+               kq->kq_state &= ~flags;
+               kqr->kqr_state |= KQR_R2K_NOTIF_ARMED;
+               kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_RECOMPUTE_WAKEUP_QOS, 0);
        }
 
-       kqwq_req_unlock(kqwq);
+       kq_req_unlock(kqwl);
 
-       /* Any events queued before we put suppressed ones back? */
-       queued_events = !kqueue_queue_empty(kq, qos_index);
-
-       /*
-        * Return suppressed knotes to their original state.
-        * For workq kqueues, suppressed ones that are still
-        * truly active (not just forced into the queue) will
-        * set flags we check below to see if anything got
-        * woken up.
-        */
-       while ((kn = TAILQ_FIRST(suppressq)) != NULL) {
-               assert(kn->kn_status & KN_SUPPRESSED);
-               knote_unsuppress(kn);
+       if (old_override) {
+               thread_drop_ipc_override(thread);
        }
 
-       kqwq_req_lock(kqwq);
-
-       /* Determine if wakeup-type events were pended during servicing */
-       pended = (kqr->kqr_state & (KQWQ_HOOKCALLED | KQWQ_WAKEUP));
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_PROCESS_END) | DBG_FUNC_END,
+                       kqwl->kqwl_dynamicid, 0, 0);
 
-       /* unbind thread thread */
-       kqworkq_unbind_thread(kqwq, qos_index, self, flags);
-
-       /* Indicate that we are done processing */
-       kqr->kqr_state &= ~(KQWQ_PROCESSING | \
-                           KQWQ_THREQUESTED | KQWQ_THMANAGER);
-
-       /*
-        * request a new thread if events have happened
-        * (not just putting stay-active events back).
-        */
-       if ((queued_events || pended) &&
-           !kqueue_queue_empty(kq, qos_index)) {
-               kqworkq_request_thread(kqwq, qos_index);
-       }
-
-       kqwq_req_unlock(kqwq);
+       return rc;
 }
 
 /*
  * Called with kqueue lock held.
  */
 static void
-kqueue_end_processing(struct kqueue *kq, kq_index_t qos_index, unsigned int flags)
+kqfile_end_processing(struct kqueue *kq)
 {
        struct knote *kn;
        struct kqtailq *suppressq;
        int procwait;
 
-       if (kq->kq_state & KQ_WORKQ) {
-               kqworkq_end_processing((struct kqworkq *)kq, qos_index, flags);
-               return;
-       }
-
-       assert(qos_index == QOS_INDEX_KQFILE);
-
-       /*
-        * Return suppressed knotes to their original state.
-        * For workq kqueues, suppressed ones that are still
-        * truly active (not just forced into the queue) will
-        * set flags we check below to see if anything got
-        * woken up.
-        */
-       suppressq = kqueue_get_suppressed_queue(kq, qos_index);
-       while ((kn = TAILQ_FIRST(suppressq)) != NULL) {
-               assert(kn->kn_status & KN_SUPPRESSED);
-               knote_unsuppress(kn);
-       }
-
-       procwait = (kq->kq_state & KQ_PROCWAIT);
-       kq->kq_state &= ~(KQ_PROCESSING | KQ_PROCWAIT);
-
-       if (procwait) {
-               /* first wake up any thread already waiting to process */
-               waitq_wakeup64_all((struct waitq *)&kq->kq_wqs,
-                                  CAST_EVENT64_T(suppressq),
-                                  THREAD_AWAKENED,
-                                  WAITQ_ALL_PRIORITIES);
-       }               
-}
-
-/*
- *     kevent_qos_internal_bind - bind thread to processing kqueue
- *
- *     Indicates that the provided thread will be responsible for
- *     servicing the particular QoS class index specified in the
- *     parameters. Once the binding is done, any overrides that may
- *     be associated with the cooresponding events can be applied.
- *
- *     This should be called as soon as the thread identity is known,
- *     preferably while still at high priority during creation.
- *
- *  - caller holds a reference on the kqueue.
- *     - the thread MUST call kevent_qos_internal after being bound
- *       or the bucket of events may never be delivered.  
- *     - Nothing locked (may take mutex or block).
- */
-
-int
-kevent_qos_internal_bind(
-       struct proc *p,
-       int qos_class,
-       thread_t thread,
-       unsigned int flags)
-{
-       struct fileproc *fp = NULL;
-       struct kqueue *kq = NULL;
-       struct kqworkq *kqwq;
-       struct kqrequest *kqr;
-       struct uthread *ut;
-       kq_index_t qos_index;
-       int res = 0;
-
-       assert(thread != THREAD_NULL);
-       assert(flags & KEVENT_FLAG_WORKQ);
-
-       if (thread == THREAD_NULL ||
-           (flags & KEVENT_FLAG_WORKQ) == 0) {
-               return EINVAL;
-       }
-
-       ut = get_bsdthread_info(thread);
-
-       /* find the kqueue */
-       res = kevent_get_kq(p, -1, flags, &fp, &kq);
-       assert(fp == NULL);
-       if (res)
-               return res;
+       kqlock_held(kq);
 
-       /* get the qos index we're going to service */
-       qos_index = qos_index_for_servicer(qos_class, thread, flags);
-       
-       /* No need to bind the manager thread to any bucket */
-       if (qos_index == KQWQ_QOS_MANAGER) {
-               assert(ut->uu_kqueue_bound == 0);
-               ut->uu_kqueue_bound = qos_index;
-               ut->uu_kqueue_flags = flags;
-               return 0;
-       }
-
-       kqlock(kq);
-       assert(kq->kq_state & KQ_WORKQ);
-       
-       kqwq = (struct kqworkq *)kq;
-       kqr = kqworkq_get_request(kqwq, qos_index);
-
-       kqwq_req_lock(kqwq);
-
-       /* 
-        * A (non-emergency) request should have been made
-        * and nobody should already be servicing this bucket.
-        */
-       assert(kqr->kqr_state & KQWQ_THREQUESTED);
-       assert((kqr->kqr_state & KQWQ_THMANAGER) == 0);
-       assert((kqr->kqr_state & KQWQ_PROCESSING) == 0);
-
-       /* Is this is an extraneous bind? */
-       if (thread == kqr->kqr_thread) {
-               assert(ut->uu_kqueue_bound == qos_index);
-               goto out;
-       }
-
-       /* nobody else bound and we're not bound elsewhere */
-       assert(ut->uu_kqueue_bound == 0);
-       assert(ut->uu_kqueue_flags == 0);
-       assert(kqr->kqr_thread == THREAD_NULL);
-
-       /* Don't bind if there is a conflict */
-       if (kqr->kqr_thread != THREAD_NULL ||
-           (kqr->kqr_state & KQWQ_THMANAGER)) {
-               res = EINPROGRESS;
-               goto out;
-       }
+       assert((kq->kq_state & (KQ_WORKQ|KQ_WORKLOOP)) == 0);
 
-       /* finally bind the thread */
-       kqr->kqr_thread = thread;
-       ut->uu_kqueue_bound = qos_index;
-       ut->uu_kqueue_flags = flags;
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQ_PROCESS_END),
+                       VM_KERNEL_UNSLIDE_OR_PERM(kq), 0);
 
-       /* add any pending overrides to the thread */
-       if (kqr->kqr_override_delta) {
-               thread_add_ipc_override(thread, qos_index + kqr->kqr_override_delta);
+       /*
+        * Return suppressed knotes to their original state.
+        */
+       suppressq = kqueue_get_suppressed_queue(kq, NULL);
+       while ((kn = TAILQ_FIRST(suppressq)) != NULL) {
+               assert(kn->kn_status & KN_SUPPRESSED);
+               knote_unsuppress(kn);
        }
 
-out:
-       kqwq_req_unlock(kqwq);
-       kqunlock(kq);
+       procwait = (kq->kq_state & KQ_PROCWAIT);
+       kq->kq_state &= ~(KQ_PROCESSING | KQ_PROCWAIT);
 
-       return res;
+       if (procwait) {
+               /* first wake up any thread already waiting to process */
+               waitq_wakeup64_all((struct waitq *)&kq->kq_wqs,
+                                  CAST_EVENT64_T(suppressq),
+                                  THREAD_AWAKENED,
+                                  WAITQ_ALL_PRIORITIES);
+       }
 }
 
-/*
- *     kevent_qos_internal_unbind - unbind thread from processing kqueue
- *
- *     End processing the per-QoS bucket of events and allow other threads
- *     to be requested for future servicing.  
- *
- *     caller holds a reference on the kqueue.
- *     thread is the current thread.
- */
-
-int
-kevent_qos_internal_unbind(
-       struct proc *p,
-       int qos_class,
-       thread_t thread,
-       unsigned int flags)
+static int
+kqueue_workloop_ctl_internal(proc_t p, uintptr_t cmd, uint64_t __unused options,
+               struct kqueue_workloop_params *params, int *retval)
 {
+       int error = 0;
+       int fd;
+       struct fileproc *fp;
        struct kqueue *kq;
-       struct uthread *ut;
-       struct fileproc *fp = NULL;
-       kq_index_t qos_index;
-       kq_index_t end_index;
-       int res;
+       struct kqworkloop *kqwl;
+       struct filedesc *fdp = p->p_fd;
+       workq_threadreq_param_t trp = { };
 
-       assert(flags & KEVENT_FLAG_WORKQ);
-       assert(thread == current_thread());
+       switch (cmd) {
+       case KQ_WORKLOOP_CREATE:
+               if (!params->kqwlp_flags) {
+                       error = EINVAL;
+                       break;
+               }
 
-       if (thread == THREAD_NULL ||
-           (flags & KEVENT_FLAG_WORKQ) == 0)
-               return EINVAL;
-           
-       /* get the kq */
-       res = kevent_get_kq(p, -1, flags, &fp, &kq);
-       assert(fp == NULL);
-       if (res)
-               return res;
+               if ((params->kqwlp_flags & KQ_WORKLOOP_CREATE_SCHED_PRI) &&
+                               (params->kqwlp_sched_pri < 1 ||
+                                params->kqwlp_sched_pri > 63 /* MAXPRI_USER */)) {
+                       error = EINVAL;
+                       break;
+               }
+
+               if ((params->kqwlp_flags & KQ_WORKLOOP_CREATE_SCHED_POL) &&
+                               invalid_policy(params->kqwlp_sched_pol)) {
+                       error = EINVAL;
+                       break;
+               }
 
-       assert(kq->kq_state & KQ_WORKQ);
+               if ((params->kqwlp_flags & KQ_WORKLOOP_CREATE_CPU_PERCENT) &&
+                               (params->kqwlp_cpu_percent <= 0 ||
+                                params->kqwlp_cpu_percent > 100 ||
+                                params->kqwlp_cpu_refillms <= 0 ||
+                                params->kqwlp_cpu_refillms > 0x00ffffff)) {
+                       error = EINVAL;
+                       break;
+               }
 
-       /* get the index we have been servicing */
-       qos_index = qos_index_for_servicer(qos_class, thread, flags);
+               if (params->kqwlp_flags & KQ_WORKLOOP_CREATE_SCHED_PRI) {
+                       trp.trp_flags |= TRP_PRIORITY;
+                       trp.trp_pri = params->kqwlp_sched_pri;
+               }
+               if (params->kqwlp_flags & KQ_WORKLOOP_CREATE_SCHED_POL) {
+                       trp.trp_flags |= TRP_POLICY;
+                       trp.trp_pol = params->kqwlp_sched_pol;
+               }
+               if (params->kqwlp_flags & KQ_WORKLOOP_CREATE_CPU_PERCENT) {
+                       trp.trp_flags |= TRP_CPUPERCENT;
+                       trp.trp_cpupercent = (uint8_t)params->kqwlp_cpu_percent;
+                       trp.trp_refillms = params->kqwlp_cpu_refillms;
+               }
 
-       ut = get_bsdthread_info(thread);
+               error = kevent_get_kq(p, params->kqwlp_id, &trp,
+                               KEVENT_FLAG_DYNAMIC_KQUEUE | KEVENT_FLAG_WORKLOOP |
+                               KEVENT_FLAG_DYNAMIC_KQ_MUST_NOT_EXIST , &fp, &fd, &kq);
+               if (error) {
+                       break;
+               }
 
-       /* early out if we were already unbound - or never bound */
-       if (ut->uu_kqueue_bound != qos_index) {
-               __assert_only struct kqworkq *kqwq = (struct kqworkq *)kq;
-               __assert_only struct kqrequest *kqr = kqworkq_get_request(kqwq, qos_index);
+               if (!(fdp->fd_flags & FD_WORKLOOP)) {
+                       /* FD_WORKLOOP indicates we've ever created a workloop
+                        * via this syscall but its only ever added to a process, never
+                        * removed.
+                        */
+                       proc_fdlock(p);
+                       fdp->fd_flags |= FD_WORKLOOP;
+                       proc_fdunlock(p);
+               }
+               break;
+       case KQ_WORKLOOP_DESTROY:
+               error = kevent_get_kq(p, params->kqwlp_id, NULL,
+                               KEVENT_FLAG_DYNAMIC_KQUEUE | KEVENT_FLAG_WORKLOOP |
+                               KEVENT_FLAG_DYNAMIC_KQ_MUST_EXIST , &fp, &fd, &kq);
+               if (error) {
+                       break;
+               }
+               kqlock(kq);
+               kqwl = (struct kqworkloop *)kq;
+               trp.trp_value = kqwl->kqwl_params;
+               if (trp.trp_flags && !(trp.trp_flags & TRP_RELEASED)) {
+                       trp.trp_flags |= TRP_RELEASED;
+                       kqueue_release(kq, KQUEUE_CANT_BE_LAST_REF);
+               } else {
+                       error = EINVAL;
+               }
+               kqunlock(kq);
+               kqueue_release_last(p, kq);
+               break;
+       }
+       *retval = 0;
+       return error;
+}
 
-               assert(ut->uu_kqueue_bound == 0);
-               assert(ut->uu_kqueue_flags == 0);
-               assert(kqr->kqr_thread != thread);
-               return EALREADY;
+int
+kqueue_workloop_ctl(proc_t p, struct kqueue_workloop_ctl_args *uap, int *retval)
+{
+       struct kqueue_workloop_params params = {
+               .kqwlp_id = 0,
+       };
+       if (uap->sz < sizeof(params.kqwlp_version)) {
+               return EINVAL;
        }
 
-       /* unbind from all the buckets we might own */
-       end_index = (qos_index == KQWQ_QOS_MANAGER) ? 
-                   0 : qos_index;
-       kqlock(kq);
-       do {
-               kqueue_end_processing(kq, qos_index, flags);
-       } while (qos_index-- > end_index);
-       kqunlock(kq);
+       size_t copyin_sz = MIN(sizeof(params), uap->sz);
+       int rv = copyin(uap->addr, &params, copyin_sz);
+       if (rv) {
+               return rv;
+       }
 
-       /* indicate that we are done processing in the uthread */
-       ut->uu_kqueue_bound = 0;
-       ut->uu_kqueue_flags = 0;
+       if (params.kqwlp_version != (int)uap->sz) {
+               return EINVAL;
+       }
 
-       return 0;
+       return kqueue_workloop_ctl_internal(p, uap->cmd, uap->options, &params,
+                       retval);
 }
 
 /*
  * kqueue_process - process the triggered events in a kqueue
  *
- *     Walk the queued knotes and validate that they are
- *     really still triggered events by calling the filter
- *     routines (if necessary).  Hold a use reference on
- *     the knote to avoid it being detached. For each event
- *     that is still considered triggered, invoke the
- *     callback routine provided.
+ *     Walk the queued knotes and validate that they are really still triggered
+ *     events by calling the filter routines (if necessary).
+ *
+ *     For each event that is still considered triggered, invoke the callback
+ *     routine provided.
  *
  *     caller holds a reference on the kqueue.
  *     kqueue locked on entry and exit - but may be dropped
  *     kqueue list locked (held for duration of call)
  */
-
 static int
 kqueue_process(struct kqueue *kq,
-    kevent_callback_t callback,
-    void *callback_data,
-    struct filt_process_s *process_data,
-    kq_index_t servicer_qos_index,
-    int *countp,
-    struct proc *p)
+               kevent_callback_t callback,
+               void *callback_data,
+               struct filt_process_s *process_data,
+               int *countp)
 {
-       unsigned int flags = process_data ? process_data->fp_flags : 0;
-       kq_index_t start_index, end_index, i;
+       struct uthread *ut = get_bsdthread_info(current_thread());
+       struct kqrequest *kqr = ut->uu_kqr_bound;
        struct knote *kn;
-       int nevents = 0;
-       int error = 0;
-
-       /*
-        * Based on the native QoS of the servicer,
-        * determine the range of QoSes that need checking
-        */
-       start_index = servicer_qos_index;
-       end_index = (start_index == KQWQ_QOS_MANAGER) ? 0 : start_index;
-       
-       i = start_index;
+       unsigned int flags = process_data ? process_data->fp_flags : 0;
+       int nevents = 0, error = 0, rc = 0;
+       struct kqtailq *base_queue, *queue;
+       kqueue_t kqu = { .kq = kq };
+#if DEBUG || DEVELOPMENT
+       int retries = 64;
+#endif
 
-       do {
-               if (kqueue_begin_processing(kq, i, flags) == -1) {
-                       *countp = 0;
-                       /* Nothing to process */
-                       continue;
+       if (kq->kq_state & KQ_WORKQ) {
+               if (kqr == NULL || (kqr->kqr_state & KQR_WORKLOOP)) {
+                       return EJUSTRETURN;
                }
+               rc = kqworkq_begin_processing(kqu.kqwq, kqr, flags);
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               if (ut->uu_kqr_bound != &kqu.kqwl->kqwl_request) {
+                       return EJUSTRETURN;
+               }
+               rc = kqworkloop_begin_processing(kqu.kqwl, flags);
+       } else {
+               rc = kqfile_begin_processing(kq);
+       }
 
-               /*
-                * loop through the enqueued knotes, processing each one and
-                * revalidating those that need it. As they are processed,
-                * they get moved to the inprocess queue (so the loop can end).
-                */
-               error = 0;
+       if (rc == -1) {
+               /* Nothing to process */
+               *countp = 0;
+               return 0;
+       }
 
-               struct kqtailq *base_queue = kqueue_get_base_queue(kq, i);
-               struct kqtailq *queue = kqueue_get_high_queue(kq, i);
-               do {
-                       while (error == 0 &&
-                              (kn = TAILQ_FIRST(queue)) != NULL) {
-                               /* Process the knote */
-                               error = knote_process(kn, callback, callback_data, process_data, p);
-                               if (error == EJUSTRETURN)
-                                       error = 0;
-                               else
-                                       nevents++;
+       /*
+        * loop through the enqueued knotes associated with this request,
+        * processing each one. Each request may have several queues
+        * of knotes to process (depending on the type of kqueue) so we
+        * have to loop through all the queues as long as we have additional
+        * space.
+        */
 
-                               /* break out if no more space for additional events */
-                               if (error == EWOULDBLOCK) {
-                                       if ((kq->kq_state & KQ_WORKQ) == 0)
-                                               kqueue_end_processing(kq, i, flags);
-                                       error = 0;
-                                       goto out;
-                               }
-                       }
-               } while (error == 0 && queue-- > base_queue);
+process_again:
+       if (kq->kq_state & KQ_WORKQ) {
+               base_queue = queue = &kqu.kqwq->kqwq_queue[kqr->kqr_qos_index];
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               base_queue = &kqu.kqwl->kqwl_queue[0];
+               queue = &kqu.kqwl->kqwl_queue[KQWL_NBUCKETS - 1];
+       } else {
+               base_queue = queue = &kq->kq_queue[QOS_INDEX_KQFILE];
+       }
 
-               /* let somebody else process events if we're not in workq mode */
-               if ((kq->kq_state & KQ_WORKQ) == 0)
-                       kqueue_end_processing(kq, i, flags);
+       do {
+               while (error == 0 && (kn = TAILQ_FIRST(queue)) != NULL) {
+                       error = knote_process(kn, callback, callback_data, process_data);
+                       if (error == EJUSTRETURN) {
+                               error = 0;
+                       } else {
+                               nevents++;
+                       }
+                       /* error is EWOULDBLOCK when the out event array is full */
+               }
 
-       } while (i-- > end_index);
+               if (error == EWOULDBLOCK) {
+                       /* break out if no more space for additional events */
+                       error = 0;
+                       break;
+               }
+       } while (queue-- > base_queue);
 
-out:
        *countp = nevents;
-       return (error);
+
+       /*
+        * If KEVENT_FLAG_PARKING is set, and no kevents have been returned,
+        * we want to unbind the kqrequest from the thread.
+        *
+        * However, because the kq locks are dropped several times during process,
+        * new knotes may have fired again, in which case, we want to fail the end
+        * processing and process again, until it converges.
+        *
+        * If we returned events however, end processing never fails.
+        */
+       if (error || nevents) flags &= ~KEVENT_FLAG_PARKING;
+       if (kq->kq_state & KQ_WORKQ) {
+               rc = kqworkq_end_processing(kqu.kqwq, kqr, flags);
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               rc = kqworkloop_end_processing(kqu.kqwl, KQ_PROCESSING, flags);
+       } else {
+               kqfile_end_processing(kq);
+               rc = 0;
+       }
+       if (rc == -1) {
+               assert(flags & KEVENT_FLAG_PARKING);
+#if DEBUG || DEVELOPMENT
+               if (retries-- == 0) {
+                       panic("kevent: way too many knote_process retries, kq: %p (0x%02x)",
+                                       kq, kq->kq_state);
+               }
+#endif
+               goto process_again;
+       }
+       return error;
 }
 
 static void
@@ -3451,7 +5462,7 @@ kqueue_scan_continue(void *data, wait_result_t wait_result)
 {
        thread_t self = current_thread();
        uthread_t ut = (uthread_t)get_bsdthread_info(self);
-       struct _kqueue_scan * cont_args = &ut->uu_kevent.ss_kqueue_scan;
+       struct _kqueue_scan * cont_args = &ut->uu_save.uus_kqueue_scan;
        struct kqueue *kq = (struct kqueue *)data;
        struct filt_process_s *process_data = cont_args->process_data;
        int error;
@@ -3462,12 +5473,17 @@ kqueue_scan_continue(void *data, wait_result_t wait_result)
        case THREAD_AWAKENED: {
                kqlock(kq);
        retry:
-               error = kqueue_process(kq, cont_args->call, cont_args->data, 
-                                      process_data, cont_args->servicer_qos_index,
-                                      &count, current_proc());
+               error = kqueue_process(kq, cont_args->call, cont_args->data,
+                                      process_data, &count);
                if (error == 0 && count == 0) {
+                       if (kq->kq_state & KQ_DRAIN) {
+                               kqunlock(kq);
+                               goto drain;
+                       }
+
                        if (kq->kq_state & KQ_WAKEUP)
                                goto retry;
+
                        waitq_assert_wait64((struct waitq *)&kq->kq_wqs,
                                            KQ_EVENT, THREAD_ABORTSAFE,
                                            cont_args->deadline);
@@ -3485,6 +5501,7 @@ kqueue_scan_continue(void *data, wait_result_t wait_result)
                error = EINTR;
                break;
        case THREAD_RESTART:
+       drain:
                error = EBADF;
                break;
        default:
@@ -3512,7 +5529,6 @@ kqueue_scan_continue(void *data, wait_result_t wait_result)
  *     The callback routine must be valid.
  *     The caller must hold a use-count reference on the kq.
  */
-
 int
 kqueue_scan(struct kqueue *kq,
            kevent_callback_t callback,
@@ -3520,10 +5536,9 @@ kqueue_scan(struct kqueue *kq,
            void *callback_data,
            struct filt_process_s *process_data,
            struct timeval *atvp,
-           struct proc *p)
+           __unused struct proc *p)
 {
        thread_continue_t cont = THREAD_CONTINUE_NULL;
-       kq_index_t servicer_qos_index;
        unsigned int flags;
        uint64_t deadline;
        int error;
@@ -3537,9 +5552,6 @@ kqueue_scan(struct kqueue *kq,
         */
        flags = (process_data) ? process_data->fp_flags : 0;
        fd = (process_data) ? process_data->fp_fd : -1;
-       servicer_qos_index = (kq->kq_state & KQ_WORKQ) ?
-           qos_index_for_servicer(fd, current_thread(), flags) :
-           QOS_INDEX_KQFILE;
 
        first = 1;
        for (;;) {
@@ -3552,8 +5564,7 @@ kqueue_scan(struct kqueue *kq,
                 */
                kqlock(kq);
                error = kqueue_process(kq, callback, callback_data,
-                                      process_data, servicer_qos_index,
-                                      &count, p);
+                                      process_data, &count);
                if (error || count)
                        break; /* lock still held */
 
@@ -3576,23 +5587,27 @@ kqueue_scan(struct kqueue *kq,
                                deadline -= now;
                                clock_absolutetime_interval_to_deadline(deadline, &deadline);
                        } else {
-                               deadline = 0;   /* block forever */
+                               deadline = 0;   /* block forever */
                        }
 
                        if (continuation) {
                                uthread_t ut = (uthread_t)get_bsdthread_info(current_thread());
-                               struct _kqueue_scan *cont_args = &ut->uu_kevent.ss_kqueue_scan;
+                               struct _kqueue_scan *cont_args = &ut->uu_save.uus_kqueue_scan;
 
                                cont_args->call = callback;
                                cont_args->cont = continuation;
                                cont_args->deadline = deadline;
                                cont_args->data = callback_data;
                                cont_args->process_data = process_data;
-                               cont_args->servicer_qos_index = servicer_qos_index;
                                cont = kqueue_scan_continue;
                        }
                }
 
+               if (kq->kq_state & KQ_DRAIN) {
+                       kqunlock(kq);
+                       return EBADF;
+               }
+
                /* If awakened during processing, try again */
                if (kq->kq_state & KQ_WAKEUP) {
                        kqunlock(kq);
@@ -3636,9 +5651,9 @@ kqueue_scan(struct kqueue *kq,
 /*ARGSUSED*/
 static int
 kqueue_read(__unused struct fileproc *fp,
-    __unused struct uio *uio,
-    __unused int flags,
-    __unused vfs_context_t ctx)
+               __unused struct uio *uio,
+               __unused int flags,
+               __unused vfs_context_t ctx)
 {
        return (ENXIO);
 }
@@ -3646,9 +5661,9 @@ kqueue_read(__unused struct fileproc *fp,
 /*ARGSUSED*/
 static int
 kqueue_write(__unused struct fileproc *fp,
-    __unused struct uio *uio,
-    __unused int flags,
-    __unused vfs_context_t ctx)
+               __unused struct uio *uio,
+               __unused int flags,
+               __unused vfs_context_t ctx)
 {
        return (ENXIO);
 }
@@ -3656,9 +5671,9 @@ kqueue_write(__unused struct fileproc *fp,
 /*ARGSUSED*/
 static int
 kqueue_ioctl(__unused struct fileproc *fp,
-    __unused u_long com,
-    __unused caddr_t data,
-    __unused vfs_context_t ctx)
+               __unused u_long com,
+               __unused caddr_t data,
+               __unused vfs_context_t ctx)
 {
        return (ENOTTY);
 }
@@ -3666,7 +5681,7 @@ kqueue_ioctl(__unused struct fileproc *fp,
 /*ARGSUSED*/
 static int
 kqueue_select(struct fileproc *fp, int which, void *wq_link_id,
-    __unused vfs_context_t ctx)
+               __unused vfs_context_t ctx)
 {
        struct kqueue *kq = (struct kqueue *)fp->f_data;
        struct kqtailq *queue;
@@ -3691,7 +5706,7 @@ kqueue_select(struct fileproc *fp, int which, void *wq_link_id,
         */
        if (wq_link_id != NULL) {
                thread_t cur_act = current_thread();
-               struct uthread * ut = get_bsdthread_info(cur_act);
+               struct uthread * ut = get_bsdthread_info(cur_act);
 
                kq->kq_state |= KQ_SEL;
                waitq_link((struct waitq *)&kq->kq_wqs, ut->uu_wqset,
@@ -3714,12 +5729,12 @@ kqueue_select(struct fileproc *fp, int which, void *wq_link_id,
                memcpy(wq_link_id, (void *)&wqptr, sizeof(void *));
        }
 
-       if (kqueue_begin_processing(kq, QOS_INDEX_KQFILE, 0) == -1) {
+       if (kqfile_begin_processing(kq) == -1) {
                kqunlock(kq);
                return (0);
        }
 
-       queue = kqueue_get_base_queue(kq, QOS_INDEX_KQFILE);
+       queue = &kq->kq_queue[QOS_INDEX_KQFILE];
        if (!TAILQ_EMPTY(queue)) {
                /*
                 * there is something queued - but it might be a
@@ -3741,25 +5756,27 @@ kqueue_select(struct fileproc *fp, int which, void *wq_link_id,
                 * There were no regular events on the queue, so take
                 * a deeper look at the stay-queued ones we suppressed.
                 */
-               suppressq = kqueue_get_suppressed_queue(kq, QOS_INDEX_KQFILE);
+               suppressq = kqueue_get_suppressed_queue(kq, NULL);
                while ((kn = (struct knote *)TAILQ_FIRST(suppressq)) != NULL) {
-                       unsigned peek = 1;
+                       KNOTE_LOCK_CTX(knlc);
+                       int result = 0;
 
                        /* If didn't vanish while suppressed - peek at it */
-                       if (kqlock2knoteuse(kq, kn)) {
+                       if ((kn->kn_status & KN_DROPPING) || !knote_lock(kq, kn, &knlc,
+                                       KNOTE_KQ_LOCK_ON_FAILURE)) {
+                               continue;
+                       }
 
-                               peek = knote_fops(kn)->f_peek(kn);
+                       result = filter_call(knote_fops(kn), f_peek(kn));
 
-                               /* if it dropped while getting lock - move on */
-                               if (!knoteuse2kqlock(kq, kn, 0))
-                                       continue;
-                       }
+                       kqlock(kq);
+                       knote_unlock(kq, kn, &knlc, KNOTE_KQ_LOCK_ALWAYS);
 
                        /* unsuppress it */
                        knote_unsuppress(kn);
 
                        /* has data or it has to report a vanish */
-                       if (peek > 0) {
+                       if (result & FILTER_ACTIVE) {
                                retnum = 1;
                                goto out;
                        }
@@ -3767,7 +5784,7 @@ kqueue_select(struct fileproc *fp, int which, void *wq_link_id,
        }
 
 out:
-       kqueue_end_processing(kq, QOS_INDEX_KQFILE, 0);
+       kqfile_end_processing(kq);
        kqunlock(kq);
        return (retnum);
 }
@@ -3787,6 +5804,13 @@ kqueue_close(struct fileglob *fg, __unused vfs_context_t ctx)
        return (0);
 }
 
+/*
+ * Max depth of the nested kq path that can be created.
+ * Note that this has to be less than the size of kq_level
+ * to avoid wrapping around and mislabeling the level.
+ */
+#define MAX_NESTED_KQ 1000
+
 /*ARGSUSED*/
 /*
  * The callers has taken a use-count reference on this kqueue and will donate it
@@ -3794,18 +5818,18 @@ kqueue_close(struct fileglob *fg, __unused vfs_context_t ctx)
  * that relationship is torn down.
  */
 static int
-kqueue_kqfilter(__unused struct fileproc *fp, struct knote *kn, __unused vfs_context_t ctx)
+kqueue_kqfilter(__unused struct fileproc *fp, struct knote *kn,
+               __unused struct kevent_internal_s *kev, __unused vfs_context_t ctx)
 {
        struct kqfile *kqf = (struct kqfile *)kn->kn_fp->f_data;
        struct kqueue *kq = &kqf->kqf_kqueue;
        struct kqueue *parentkq = knote_get_kq(kn);
+       uint16_t plevel = 0;
 
        assert((kqf->kqf_state & KQ_WORKQ) == 0);
 
-       if (parentkq == kq ||
-           kn->kn_filter != EVFILT_READ) {
-               kn->kn_flags = EV_ERROR;
-               kn->kn_data = EINVAL;
+       if (parentkq == kq || kn->kn_filter != EVFILT_READ) {
+               knote_set_error(kn, EINVAL);
                return 0;
        }
 
@@ -3818,6 +5842,8 @@ kqueue_kqfilter(__unused struct fileproc *fp, struct knote *kn, __unused vfs_con
         * into another kqueue at a lower level than the potenial
         * child (because it could indicate a cycle).  If that test
         * passes, we just mark the nesting levels accordingly.
+        *
+        * Only up to MAX_NESTED_KQ can be nested.
         */
 
        kqlock(parentkq);
@@ -3825,15 +5851,21 @@ kqueue_kqfilter(__unused struct fileproc *fp, struct knote *kn, __unused vfs_con
            parentkq->kq_level < kq->kq_level)
        {
                kqunlock(parentkq);
-               kn->kn_flags = EV_ERROR;
-               kn->kn_data = EINVAL;
+               knote_set_error(kn, EINVAL);
                return 0;
        } else {
                /* set parent level appropriately */
-               if (parentkq->kq_level == 0)
-                       parentkq->kq_level = 2;
-               if (parentkq->kq_level < kq->kq_level + 1)
-                       parentkq->kq_level = kq->kq_level + 1;
+               plevel = (parentkq->kq_level == 0)? 2: parentkq->kq_level;
+               if (plevel < kq->kq_level + 1) {
+                       if (kq->kq_level + 1 > MAX_NESTED_KQ) {
+                               kqunlock(parentkq);
+                               knote_set_error(kn, EINVAL);
+                               return 0;
+                       }
+                       plevel = kq->kq_level + 1;
+               }
+
+               parentkq->kq_level = plevel;
                kqunlock(parentkq);
 
                kn->kn_filtid = EVFILTID_KQREAD;
@@ -3889,82 +5921,291 @@ kqueue_stat(struct kqueue *kq, void *ub, int isstat64, proc_t p)
                        sb64->st_blksize = sizeof(struct user32_kevent);
                sb64->st_mode = S_IFIFO;
        } else {
-               struct stat *sb = (struct stat *)ub;
+               struct stat *sb = (struct stat *)ub;
+
+               bzero((void *)sb, sizeof(*sb));
+               sb->st_size = kq->kq_count;
+               if (kq->kq_state & KQ_KEV_QOS)
+                       sb->st_blksize = sizeof(struct kevent_qos_s);
+               else if (kq->kq_state & KQ_KEV64)
+                       sb->st_blksize = sizeof(struct kevent64_s);
+               else if (IS_64BIT_PROCESS(p))
+                       sb->st_blksize = sizeof(struct user64_kevent);
+               else
+                       sb->st_blksize = sizeof(struct user32_kevent);
+               sb->st_mode = S_IFIFO;
+       }
+       kqunlock(kq);
+       return (0);
+}
+
+/*
+ * Interact with the pthread kext to request a servicing there at a specific QoS
+ * level.
+ *
+ * - Caller holds the workq request lock
+ *
+ * - May be called with the kqueue's wait queue set locked,
+ *   so cannot do anything that could recurse on that.
+ */
+static void
+kqueue_threadreq_initiate(struct kqueue *kq, struct kqrequest *kqr,
+               kq_index_t qos, int flags)
+{
+       assert(kqr->kqr_state & KQR_WAKEUP);
+       assert(kqr->kqr_thread == THREAD_NULL);
+       assert((kqr->kqr_state & KQR_THREQUESTED) == 0);
+       struct turnstile *ts = TURNSTILE_NULL;
+
+       if (workq_is_exiting(kq->kq_p)) {
+               return;
+       }
+
+       /* Add a thread request reference on the kqueue. */
+       kqueue_retain(kq);
+
+       kq_req_held(kq);
+
+       if (kq->kq_state & KQ_WORKLOOP) {
+               __assert_only struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+
+               assert(kqwl->kqwl_owner == THREAD_NULL);
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_THREQUEST),
+                               kqwl->kqwl_dynamicid, 0, qos, kqr->kqr_state);
+               ts = kqwl->kqwl_turnstile;
+       } else {
+               assert(kq->kq_state & KQ_WORKQ);
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWQ_THREQUEST),
+                               -1, 0, qos, kqr->kqr_state);
+       }
+
+       kqr->kqr_state |= KQR_THREQUESTED;
+
+       /*
+        * New-style thread request supported.
+        * Provide the pthread kext a pointer to a workq_threadreq_s structure for
+        * its use until a corresponding kqueue_threadreq_bind callback.
+        */
+#if 0 // 45129862
+       if ((kq->kq_state & KQ_WORKLOOP) && current_proc() == kq->kq_p) {
+               flags |= WORKQ_THREADREQ_SET_AST_ON_FAILURE;
+       }
+#endif
+       if (qos == KQWQ_QOS_MANAGER) {
+               qos = WORKQ_THREAD_QOS_MANAGER;
+       }
+       if (!workq_kern_threadreq_initiate(kq->kq_p, kqr, ts, qos, flags)) {
+               /*
+                * Process is shutting down or exec'ing.
+                * All the kqueues are going to be cleaned up
+                * soon. Forget we even asked for a thread -
+                * and make sure we don't ask for more.
+                */
+               kqr->kqr_state &= ~(KQR_THREQUESTED | KQR_R2K_NOTIF_ARMED);
+               kqueue_release(kq, KQUEUE_CANT_BE_LAST_REF);
+       }
+}
+
+/*
+ * kqueue_threadreq_bind_prepost - prepost the bind to kevent
+ *
+ * This is used when kqueue_threadreq_bind may cause a lock inversion.
+ */
+void
+kqueue_threadreq_bind_prepost(struct proc *p __unused, workq_threadreq_t req,
+               thread_t thread)
+{
+       struct kqrequest *kqr = __container_of(req, struct kqrequest, kqr_req);
+       struct uthread *ut = get_bsdthread_info(thread);
+
+       req->tr_binding_thread = thread;
+       ut->uu_kqr_bound = kqr;
+       req->tr_state = TR_STATE_BINDING;
+
+       struct kqworkloop *kqwl = kqr_kqworkloop(kqr);
+       if (kqwl && kqwl->kqwl_turnstile) {
+               struct turnstile *ts = kqwl->kqwl_turnstile;
+               /*
+                * While a thread request is in flight, the workqueue
+                * is the interlock for the turnstile and can update the inheritor.
+                */
+               turnstile_update_inheritor(ts, thread, TURNSTILE_IMMEDIATE_UPDATE |
+                               TURNSTILE_INHERITOR_THREAD);
+               turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_HELD);
+       }
+}
+
+/*
+ * kqueue_threadreq_bind_commit - commit a bind prepost
+ *
+ * The workq code has to commit any binding prepost before the thread has
+ * a chance to come back to userspace (and do kevent syscalls) or be aborted.
+ */
+void
+kqueue_threadreq_bind_commit(struct proc *p, thread_t thread)
+{
+       struct uthread *ut = get_bsdthread_info(thread);
+       struct kqrequest *kqr = ut->uu_kqr_bound;
+       kqueue_t kqu = kqr_kqueue(p, kqr);
+
+       kq_req_lock(kqu);
+       if (kqr->kqr_req.tr_state == TR_STATE_BINDING) {
+               kqueue_threadreq_bind(p, &kqr->kqr_req, thread, 0);
+       }
+       kq_req_unlock(kqu);
+}
+
+static void
+kqueue_threadreq_modify(struct kqueue *kq, struct kqrequest *kqr, kq_index_t qos)
+{
+       assert(kqr->kqr_state & KQR_THREQUESTED);
+       assert(kqr->kqr_thread == THREAD_NULL);
+
+       kq_req_held(kq);
+
+       int flags = 0;
+#if 0 // 45129862
+       if ((kq->kq_state & KQ_WORKLOOP) && kq->kq_p == current_proc()) {
+               flags |= WORKQ_THREADREQ_SET_AST_ON_FAILURE;
+       }
+#endif
+       workq_kern_threadreq_modify(kq->kq_p, kqr, qos, flags);
+}
+
+/*
+ * kqueue_threadreq_bind - bind thread to processing kqrequest
+ *
+ * The provided thread will be responsible for delivering events
+ * associated with the given kqrequest.  Bind it and get ready for
+ * the thread to eventually arrive.
+ */
+void
+kqueue_threadreq_bind(struct proc *p, workq_threadreq_t req, thread_t thread,
+               unsigned int flags)
+{
+       struct kqrequest *kqr = __container_of(req, struct kqrequest, kqr_req);
+       kqueue_t kqu = kqr_kqueue(p, kqr);
+       struct uthread *ut = get_bsdthread_info(thread);
+
+       kq_req_held(kqu);
+
+       assert(kqr->kqr_state & KQR_THREQUESTED);
+       assert(kqr->kqr_thread == THREAD_NULL);
+       assert(ut->uu_kqueue_override == 0);
+
+       if (kqr->kqr_req.tr_state == TR_STATE_BINDING) {
+               assert(ut->uu_kqr_bound == kqr);
+               assert(kqr->kqr_req.tr_binding_thread == thread);
+               kqr->kqr_req.tr_state = TR_STATE_IDLE;
+               kqr->kqr_req.tr_binding_thread = NULL;
+       } else {
+               assert(ut->uu_kqr_bound == NULL);
+       }
+
+       ut->uu_kqr_bound = kqr;
+       kqr->kqr_thread = thread;
+
+       if (kqu.kq->kq_state & KQ_WORKLOOP) {
+               struct turnstile *ts = kqu.kqwl->kqwl_turnstile;
+
+               if (__improbable(thread == kqu.kqwl->kqwl_owner)) {
+                       /*
+                        * <rdar://problem/38626999> shows that asserting here is not ok.
+                        *
+                        * This is not supposed to happen for correct use of the interface,
+                        * but it is sadly possible for userspace (with the help of memory
+                        * corruption, such as over-release of a dispatch queue) to make
+                        * the creator thread the "owner" of a workloop.
+                        *
+                        * Once that happens, and that creator thread picks up the same
+                        * workloop as a servicer, we trip this codepath. We need to fixup
+                        * the state to forget about this thread being the owner, as the
+                        * entire workloop state machine expects servicers to never be
+                        * owners and everything would basically go downhill from here.
+                        */
+                       kqu.kqwl->kqwl_owner = THREAD_NULL;
+                       if (kqworkloop_owner_override(kqu.kqwl)) {
+                               thread_drop_ipc_override(thread);
+                       }
+                       thread_ends_owning_workloop(thread);
+               }
+
+               if (ts && (flags & KQUEUE_THREADERQ_BIND_NO_INHERITOR_UPDATE) == 0) {
+                       /*
+                        * Past this point, the interlock is the kq req lock again,
+                        * so we can fix the inheritor for good.
+                        */
+                       filt_wlupdate_inheritor(kqu.kqwl, ts, TURNSTILE_IMMEDIATE_UPDATE);
+                       turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_HELD);
+               }
+
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_BIND), kqu.kqwl->kqwl_dynamicid,
+                               thread_tid(thread), kqr->kqr_qos_index,
+                               (kqr->kqr_override_index << 16) | kqr->kqr_state);
+
+               ut->uu_kqueue_override = kqr->kqr_override_index;
+               if (kqr->kqr_override_index) {
+                       thread_add_ipc_override(thread, kqr->kqr_override_index);
+               }
+       } else {
+               assert(kqr->kqr_override_index == 0);
 
-               bzero((void *)sb, sizeof(*sb));
-               sb->st_size = kq->kq_count;
-               if (kq->kq_state & KQ_KEV_QOS)
-                       sb->st_blksize = sizeof(struct kevent_qos_s);
-               else if (kq->kq_state & KQ_KEV64)
-                       sb->st_blksize = sizeof(struct kevent64_s);
-               else if (IS_64BIT_PROCESS(p))
-                       sb->st_blksize = sizeof(struct user64_kevent);
-               else
-                       sb->st_blksize = sizeof(struct user32_kevent);
-               sb->st_mode = S_IFIFO;
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWQ_BIND), -1,
+                               thread_tid(thread), kqr->kqr_qos_index,
+                               (kqr->kqr_override_index << 16) | kqr->kqr_state);
        }
-       kqunlock(kq);
-       return (0);
 }
 
-
 /*
- * Interact with the pthread kext to request a servicing there.
- * Eventually, this will request threads at specific QoS levels.
- * For now, it only requests a dispatch-manager-QoS thread, and
- * only one-at-a-time.
- *
- * - Caller holds the workq request lock
+ * kqueue_threadreq_cancel - abort a pending thread request
  *
- * - May be called with the kqueue's wait queue set locked,
- *   so cannot do anything that could recurse on that.
+ * Called when exiting/exec'ing. Forget our pending request.
  */
-static void
-kqworkq_request_thread(
-       struct kqworkq *kqwq, 
-       kq_index_t qos_index)
+void
+kqueue_threadreq_cancel(struct proc *p, workq_threadreq_t req)
 {
-       struct kqrequest *kqr;
+       struct kqrequest *kqr = __container_of(req, struct kqrequest, kqr_req);
+       kqueue_t kqu = kqr_kqueue(p, kqr);
 
-       assert(kqwq->kqwq_state & KQ_WORKQ);
-       assert(qos_index < KQWQ_NQOS);
-
-       kqr = kqworkq_get_request(kqwq, qos_index);
-
-       /* 
-        * If we have already requested a thread, and it hasn't
-        * started processing yet, there's no use hammering away
-        * on the pthread kext.
-        */
-       if (kqr->kqr_state & KQWQ_THREQUESTED)
-               return;
+       kq_req_lock(kqu);
 
        assert(kqr->kqr_thread == THREAD_NULL);
+       assert(kqr->kqr_state & KQR_THREQUESTED);
+       kqr->kqr_state &= ~(KQR_THREQUESTED | KQR_R2K_NOTIF_ARMED);
 
-       /* request additional workq threads if appropriate */
-       if (pthread_functions != NULL &&
-           pthread_functions->workq_reqthreads != NULL) {
-               unsigned int flags = KEVENT_FLAG_WORKQ;
+       kq_req_unlock(kqu);
 
-               /* Compute a priority based on qos_index. */
-               struct workq_reqthreads_req_s request = {
-                       .priority = qos_from_qos_index(qos_index),
-                       .count = 1
-               };
+       kqueue_release_last(p, kqu); /* may dealloc kqu */
+}
 
-               thread_t wqthread;
-               wqthread = (*pthread_functions->workq_reqthreads)(kqwq->kqwq_p, 1, &request);
-               kqr->kqr_state |= KQWQ_THREQUESTED;
+workq_threadreq_param_t
+kqueue_threadreq_workloop_param(workq_threadreq_t req)
+{
+       struct kqrequest *kqr = __container_of(req, struct kqrequest, kqr_req);
+       struct kqworkloop *kqwl;
+       workq_threadreq_param_t trp;
 
-               /* Have we been switched to the emergency/manager thread? */
-               if (wqthread == (thread_t)-1) {
-                       flags |= KEVENT_FLAG_WORKQ_MANAGER;
-                       wqthread = THREAD_NULL;
-               } else if (qos_index == KQWQ_QOS_MANAGER)
-                       flags |= KEVENT_FLAG_WORKQ_MANAGER;
+       assert(kqr->kqr_state & KQR_WORKLOOP);
+       kqwl = __container_of(kqr, struct kqworkloop, kqwl_request);
+       trp.trp_value = kqwl->kqwl_params;
+       return trp;
+}
 
-               /* bind the thread */
-               kqworkq_bind_thread(kqwq, qos_index, wqthread, flags);
+/*
+ *     kqueue_threadreq_unbind - unbind thread from processing kqueue
+ *
+ *     End processing the per-QoS bucket of events and allow other threads
+ *     to be requested for future servicing.
+ *
+ *     caller holds a reference on the kqueue.
+ */
+void
+kqueue_threadreq_unbind(struct proc *p, struct kqrequest *kqr)
+{
+       if (kqr->kqr_state & KQR_WORKLOOP) {
+               kqworkloop_unbind(p, kqr_kqworkloop(kqr));
+       } else {
+               kqworkq_unbind(p, kqr);
        }
 }
 
@@ -3978,152 +6219,438 @@ kqworkq_request_thread(
  *   so cannot do anything that could recurse on that.
  */
 static void
-kqworkq_request_help(
-       struct kqworkq *kqwq, 
-       kq_index_t qos_index,
-       uint32_t type)
+kqworkq_request_help(struct kqworkq *kqwq, kq_index_t qos_index)
 {
        struct kqrequest *kqr;
 
        /* convert to thread qos value */
-       assert(qos_index < KQWQ_NQOS);
-       
-       kqwq_req_lock(kqwq);
+       assert(qos_index < KQWQ_NBUCKETS);
+
+       kq_req_lock(kqwq);
        kqr = kqworkq_get_request(kqwq, qos_index);
 
+       if ((kqr->kqr_state & KQR_WAKEUP) == 0) {
+               kqr->kqr_state |= KQR_WAKEUP;
+               if ((kqr->kqr_state & KQR_THREQUESTED) == 0) {
+                       kqueue_threadreq_initiate(&kqwq->kqwq_kqueue, kqr, qos_index, 0);
+               }
+       }
+       kq_req_unlock(kqwq);
+}
+
+static kq_index_t
+kqworkloop_owner_override(struct kqworkloop *kqwl)
+{
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       return MAX(kqr->kqr_qos_index, kqr->kqr_override_index);
+}
+
+static inline void
+kqworkloop_request_fire_r2k_notification(struct kqworkloop *kqwl)
+{
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+
+       kq_req_held(kqwl);
+
+       if (kqr->kqr_state & KQR_R2K_NOTIF_ARMED) {
+               assert(kqr->kqr_thread);
+               kqr->kqr_state &= ~KQR_R2K_NOTIF_ARMED;
+               act_set_astkevent(kqr->kqr_thread, AST_KEVENT_RETURN_TO_KERNEL);
+       }
+}
+
+static void
+kqworkloop_update_threads_qos(struct kqworkloop *kqwl, int op, kq_index_t qos)
+{
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       struct kqueue *kq = &kqwl->kqwl_kqueue;
+       kq_index_t old_owner_override = kqworkloop_owner_override(kqwl);
+       kq_index_t i;
+
+       /* must hold the kqr lock */
+       kq_req_held(kqwl);
+
+       switch (op) {
+       case KQWL_UTQ_UPDATE_WAKEUP_QOS:
+               if (qos == KQWL_BUCKET_STAYACTIVE) {
+                       /*
+                        * the KQWL_BUCKET_STAYACTIVE is not a QoS bucket, we only remember
+                        * a high watermark (kqr_stayactive_qos) of any stay active knote
+                        * that was ever registered with this workloop.
+                        *
+                        * When waitq_set__CALLING_PREPOST_HOOK__() wakes up any stay active
+                        * knote, we use this high-watermark as a wakeup-index, and also set
+                        * the magic KQWL_BUCKET_STAYACTIVE bit to make sure we remember
+                        * there is at least one stay active knote fired until the next full
+                        * processing of this bucket.
+                        */
+                       kqr->kqr_wakeup_indexes |= KQWL_STAYACTIVE_FIRED_BIT;
+                       qos = kqr->kqr_stayactive_qos;
+                       assert(qos);
+               }
+               if (kqr->kqr_wakeup_indexes & (1 << qos)) {
+                       assert(kqr->kqr_state & KQR_WAKEUP);
+                       break;
+               }
+
+               kqr->kqr_wakeup_indexes |= (1 << qos);
+               kqr->kqr_state |= KQR_WAKEUP;
+               kqworkloop_request_fire_r2k_notification(kqwl);
+               goto recompute;
+
+       case KQWL_UTQ_UPDATE_STAYACTIVE_QOS:
+               assert(qos);
+               if (kqr->kqr_stayactive_qos < qos) {
+                       kqr->kqr_stayactive_qos = qos;
+                       if (kqr->kqr_wakeup_indexes & KQWL_STAYACTIVE_FIRED_BIT) {
+                               assert(kqr->kqr_state & KQR_WAKEUP);
+                               kqr->kqr_wakeup_indexes |= (1 << qos);
+                               goto recompute;
+                       }
+               }
+               break;
+
+       case KQWL_UTQ_PARKING:
+       case KQWL_UTQ_UNBINDING:
+               kqr->kqr_override_index = qos;
+               /* FALLTHROUGH */
+       case KQWL_UTQ_RECOMPUTE_WAKEUP_QOS:
+               if (op == KQWL_UTQ_RECOMPUTE_WAKEUP_QOS) {
+                       assert(qos == THREAD_QOS_UNSPECIFIED);
+               }
+               kqlock_held(kqwl); // to look at kq_queues
+               i = KQWL_BUCKET_STAYACTIVE;
+               if (TAILQ_EMPTY(&kqr->kqr_suppressed)) {
+                       kqr->kqr_override_index = THREAD_QOS_UNSPECIFIED;
+               }
+               if (!TAILQ_EMPTY(&kqwl->kqwl_queue[i]) &&
+                               (kqr->kqr_wakeup_indexes & KQWL_STAYACTIVE_FIRED_BIT)) {
+                       /*
+                        * If the KQWL_STAYACTIVE_FIRED_BIT is set, it means a stay active
+                        * knote may have fired, so we need to merge in kqr_stayactive_qos.
+                        *
+                        * Unlike other buckets, this one is never empty but could be idle.
+                        */
+                       kqr->kqr_wakeup_indexes &= KQWL_STAYACTIVE_FIRED_BIT;
+                       kqr->kqr_wakeup_indexes |= (1 << kqr->kqr_stayactive_qos);
+               } else {
+                       kqr->kqr_wakeup_indexes = 0;
+               }
+               for (i = THREAD_QOS_UNSPECIFIED + 1; i < KQWL_BUCKET_STAYACTIVE; i++) {
+                       if (!TAILQ_EMPTY(&kqwl->kqwl_queue[i])) {
+                               kqr->kqr_wakeup_indexes |= (1 << i);
+                       }
+               }
+               if (kqr->kqr_wakeup_indexes) {
+                       kqr->kqr_state |= KQR_WAKEUP;
+                       kqworkloop_request_fire_r2k_notification(kqwl);
+               } else {
+                       kqr->kqr_state &= ~KQR_WAKEUP;
+               }
+               goto recompute;
+
+       case KQWL_UTQ_RESET_WAKEUP_OVERRIDE:
+               kqr->kqr_override_index = qos;
+               goto recompute;
+
+       case KQWL_UTQ_UPDATE_WAKEUP_OVERRIDE:
+       recompute:
+               /*
+                * When modifying the wakeup QoS or the override QoS, we always need to
+                * maintain our invariant that kqr_override_index is at least as large
+                * as the highest QoS for which an event is fired.
+                *
+                * However this override index can be larger when there is an overriden
+                * suppressed knote pushing on the kqueue.
+                */
+               if (kqr->kqr_wakeup_indexes > (1 << qos)) {
+                       qos = fls(kqr->kqr_wakeup_indexes) - 1; /* fls is 1-based */
+               }
+               if (kqr->kqr_override_index < qos) {
+                       kqr->kqr_override_index = qos;
+               }
+               break;
+
+       case KQWL_UTQ_REDRIVE_EVENTS:
+               break;
+
+       case KQWL_UTQ_SET_QOS_INDEX:
+               kqr->kqr_qos_index = qos;
+               break;
+
+       default:
+               panic("unknown kqwl thread qos update operation: %d", op);
+       }
+
+       thread_t kqwl_owner = kqwl->kqwl_owner;
+       thread_t servicer = kqr->kqr_thread;
+       boolean_t qos_changed = FALSE;
+       kq_index_t new_owner_override = kqworkloop_owner_override(kqwl);
+
        /*
-        * If someone is processing the queue, just mark what type
-        * of attempt this was (from a kq wakeup or from a waitq hook).
-        * They'll be noticed at the end of servicing and a new thread
-        * will be requested at that point.
+        * Apply the diffs to the owner if applicable
         */
-       if (kqr->kqr_state & KQWQ_PROCESSING) {
-               kqr->kqr_state |= type;
-               kqwq_req_unlock(kqwq);
-               return;
+       if (kqwl_owner) {
+#if 0
+               /* JMM - need new trace hooks for owner overrides */
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_THADJUST),
+                               kqwl->kqwl_dynamicid, thread_tid(kqwl_owner), kqr->kqr_qos_index,
+                               (kqr->kqr_override_index << 16) | kqr->kqr_state);
+#endif
+               if (new_owner_override == old_owner_override) {
+                       // nothing to do
+               } else if (old_owner_override == THREAD_QOS_UNSPECIFIED) {
+                       thread_add_ipc_override(kqwl_owner, new_owner_override);
+               } else if (new_owner_override == THREAD_QOS_UNSPECIFIED) {
+                       thread_drop_ipc_override(kqwl_owner);
+               } else /*  old_owner_override != new_owner_override */ {
+                       thread_update_ipc_override(kqwl_owner, new_owner_override);
+               }
        }
 
-       kqworkq_request_thread(kqwq, qos_index);
-       kqwq_req_unlock(kqwq);
-}
+       /*
+        * apply the diffs to the servicer
+        */
+       if ((kqr->kqr_state & KQR_THREQUESTED) == 0) {
+               /*
+                * No servicer, nor thread-request
+                *
+                * Make a new thread request, unless there is an owner (or the workloop
+                * is suspended in userland) or if there is no asynchronous work in the
+                * first place.
+                */
 
-/*
- * These arrays described the low and high qindexes for a given qos_index.
- * The values come from the chart in <sys/eventvar.h> (must stay in sync).
- */
-static kq_index_t _kq_base_index[KQWQ_NQOS] = {0, 0, 6, 11, 15, 18, 20, 21};
-static kq_index_t _kq_high_index[KQWQ_NQOS] = {0, 5, 10, 14, 17, 19, 20, 21};
+               if (kqwl_owner == NULL && (kqr->kqr_state & KQR_WAKEUP)) {
+                       int initiate_flags = 0;
+                       if (op == KQWL_UTQ_UNBINDING) {
+                               initiate_flags = WORKQ_THREADREQ_ATTEMPT_REBIND;
+                       }
+                       kqueue_threadreq_initiate(kq, kqr, new_owner_override,
+                                       initiate_flags);
+               }
+       } else if (servicer) {
+               /*
+                * Servicer in flight
+                *
+                * Just apply the diff to the servicer
+                */
+               struct uthread *ut = get_bsdthread_info(servicer);
+               if (ut->uu_kqueue_override != kqr->kqr_override_index) {
+                       if (ut->uu_kqueue_override == THREAD_QOS_UNSPECIFIED) {
+                               thread_add_ipc_override(servicer, kqr->kqr_override_index);
+                       } else if (kqr->kqr_override_index == THREAD_QOS_UNSPECIFIED) {
+                               thread_drop_ipc_override(servicer);
+                       } else /* ut->uu_kqueue_override != kqr->kqr_override_index */ {
+                               thread_update_ipc_override(servicer, kqr->kqr_override_index);
+                       }
+                       ut->uu_kqueue_override = kqr->kqr_override_index;
+                       qos_changed = TRUE;
+               }
+       } else if (new_owner_override == THREAD_QOS_UNSPECIFIED) {
+               /*
+                * No events to deliver anymore.
+                *
+                * However canceling with turnstiles is challenging, so the fact that
+                * the request isn't useful will be discovered by the servicer himself
+                * later on.
+                */
+       } else if (old_owner_override != new_owner_override) {
+               /*
+                * Request is in flight
+                *
+                * Apply the diff to the thread request
+                */
+               kqueue_threadreq_modify(kq, kqr, new_owner_override);
+               qos_changed = TRUE;
+       }
 
-static struct kqtailq *
-kqueue_get_base_queue(struct kqueue *kq, kq_index_t qos_index)
+       if (qos_changed) {
+               KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_THADJUST), kqwl->kqwl_dynamicid,
+                               thread_tid(kqr->kqr_thread), kqr->kqr_qos_index,
+                               (kqr->kqr_override_index << 16) | kqr->kqr_state);
+       }
+}
+
+static void
+kqworkloop_request_help(struct kqworkloop *kqwl, kq_index_t qos_index)
 {
-       assert(qos_index < KQWQ_NQOS);
-       return &kq->kq_queue[_kq_base_index[qos_index]];
+       /* convert to thread qos value */
+       assert(qos_index < KQWL_NBUCKETS);
+
+       kq_req_lock(kqwl);
+       kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_UPDATE_WAKEUP_QOS, qos_index);
+       kq_req_unlock(kqwl);
 }
 
 static struct kqtailq *
-kqueue_get_high_queue(struct kqueue *kq, kq_index_t qos_index)
+kqueue_get_queue(struct kqueue *kq, kq_index_t qos_index)
 {
-       assert(qos_index < KQWQ_NQOS);
-       return &kq->kq_queue[_kq_high_index[qos_index]];
+       if (kq->kq_state & KQ_WORKQ) {
+               assert(qos_index < KQWQ_NBUCKETS);
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               assert(qos_index < KQWL_NBUCKETS);
+       } else {
+               assert(qos_index == QOS_INDEX_KQFILE);
+       }
+       static_assert(offsetof(struct kqueue, kq_queue) == sizeof(struct kqueue),
+                       "struct kqueue::kq_queue must be exactly at the end");
+       return &kq->kq_queue[qos_index];
 }
 
 static int
 kqueue_queue_empty(struct kqueue *kq, kq_index_t qos_index)
 {
-       struct kqtailq *base_queue = kqueue_get_base_queue(kq, qos_index);
-       struct kqtailq *queue = kqueue_get_high_queue(kq, qos_index);
-
-       do {
-               if (!TAILQ_EMPTY(queue))
-                       return 0;
-       } while (queue-- > base_queue);
-       return 1;
+       return TAILQ_EMPTY(kqueue_get_queue(kq, qos_index));
 }
 
 static struct kqtailq *
-kqueue_get_suppressed_queue(struct kqueue *kq, kq_index_t qos_index)
+kqueue_get_suppressed_queue(kqueue_t kq, struct knote *kn)
 {
-       if (kq->kq_state & KQ_WORKQ) {
-               struct kqworkq *kqwq = (struct kqworkq *)kq;
-               struct kqrequest *kqr;
-
-               kqr = kqworkq_get_request(kqwq, qos_index);
-               return &kqr->kqr_suppressed;
+       if (kq.kq->kq_state & KQ_WORKQ) {
+               return &kqworkq_get_request(kq.kqwq, kn->kn_qos_index)->kqr_suppressed;
+       } else if (kq.kq->kq_state & KQ_WORKLOOP) {
+               return &kq.kqwl->kqwl_request.kqr_suppressed;
        } else {
-               struct kqfile *kqf = (struct kqfile *)kq;
-               return &kqf->kqf_suppressed;
+               return &kq.kqf->kqf_suppressed;
        }
 }
 
-static kq_index_t
-knote_get_queue_index(struct knote *kn)
+static struct turnstile *
+kqueue_get_turnstile(kqueue_t kqu, bool can_alloc)
 {
-       kq_index_t override_index = knote_get_qos_override_index(kn);
-       kq_index_t qos_index = knote_get_qos_index(kn);
-       struct kqueue *kq = knote_get_kq(kn);
-       kq_index_t res;
+       uint8_t kqr_state;
 
-       if ((kq->kq_state & KQ_WORKQ) == 0) {
-               assert(qos_index == 0);
-               assert(override_index == 0);
+       if ((kqu.kq->kq_state & KQ_WORKLOOP) == 0) {
+               return TURNSTILE_NULL;
        }
-       res = _kq_base_index[qos_index];
-       if (override_index > qos_index)
-               res += override_index - qos_index;
 
-       assert(res <= _kq_high_index[qos_index]);
-       return res;
-}
+       kqr_state = os_atomic_load(&kqu.kqwl->kqwl_request.kqr_state, relaxed);
+       if (kqr_state & KQR_ALLOCATED_TURNSTILE) {
+               /* force a dependency to pair with the atomic or with release below */
+               return os_atomic_load_with_dependency_on(&kqu.kqwl->kqwl_turnstile,
+                               kqr_state);
+       }
 
-static struct kqtailq *
-knote_get_queue(struct knote *kn)
-{
-       kq_index_t qindex = knote_get_queue_index(kn);
+       if (!can_alloc) {
+               return TURNSTILE_NULL;
+       }
+
+       struct turnstile *ts = turnstile_alloc(), *free_ts = TURNSTILE_NULL;
+
+       kq_req_lock(kqu);
+       if (filt_wlturnstile_interlock_is_workq(kqu.kqwl)) {
+               workq_kern_threadreq_lock(kqu.kqwl->kqwl_p);
+       }
+
+       if (kqu.kqwl->kqwl_request.kqr_state & KQR_ALLOCATED_TURNSTILE) {
+               free_ts = ts;
+               ts = kqu.kqwl->kqwl_turnstile;
+       } else {
+               ts = turnstile_prepare((uintptr_t)kqu.kqwl, &kqu.kqwl->kqwl_turnstile,
+                               ts, TURNSTILE_WORKLOOPS);
+
+               /* release-barrier to pair with the unlocked load of kqwl_turnstile above */
+               os_atomic_or(&kqu.kqwl->kqwl_request.kqr_state,
+                               KQR_ALLOCATED_TURNSTILE, release);
+       }
+
+       if (filt_wlturnstile_interlock_is_workq(kqu.kqwl)) {
+               workq_kern_threadreq_unlock(kqu.kqwl->kqwl_p);
+       }
+       kq_req_unlock(kqu.kqwl);
 
-       return &(knote_get_kq(kn))->kq_queue[qindex];
+       if (free_ts) {
+               turnstile_deallocate(free_ts);
+       }
+       return ts;
 }
 
-static struct kqtailq *
-knote_get_suppressed_queue(struct knote *kn)
+struct turnstile *
+kqueue_turnstile(struct kqueue *kq)
 {
-       kq_index_t qos_index = knote_get_qos_index(kn);
-       struct kqueue *kq = knote_get_kq(kn);
-
-       return kqueue_get_suppressed_queue(kq, qos_index);
+       return kqueue_get_turnstile(kq, false);
 }
 
-static kq_index_t
-knote_get_req_index(struct knote *kn)
+struct turnstile *
+kqueue_alloc_turnstile(struct kqueue *kq)
 {
-       return kn->kn_req_index;
+       return kqueue_get_turnstile(kq, true);
 }
 
-static kq_index_t
-knote_get_qos_index(struct knote *kn)
+static struct kqtailq *
+knote_get_queue(struct knote *kn)
 {
-       return kn->kn_qos_index;
+       return kqueue_get_queue(knote_get_kq(kn), kn->kn_qos_index);
 }
 
 static void
-knote_set_qos_index(struct knote *kn, kq_index_t qos_index)
+knote_reset_priority(struct knote *kn, pthread_priority_t pp)
 {
        struct kqueue *kq = knote_get_kq(kn);
+       kq_index_t qos = _pthread_priority_thread_qos(pp);
 
-       assert(qos_index < KQWQ_NQOS);
        assert((kn->kn_status & KN_QUEUED) == 0);
 
-       if (kq->kq_state & KQ_WORKQ)
-               assert(qos_index > QOS_INDEX_KQFILE);
-       else
-               assert(qos_index == QOS_INDEX_KQFILE);
+       if (kq->kq_state & KQ_WORKQ) {
+               if (qos == THREAD_QOS_UNSPECIFIED) {
+                       /* On workqueues, outside of QoS means MANAGER */
+                       qos = KQWQ_QOS_MANAGER;
+                       pp = _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG;
+               } else {
+                       pp = _pthread_priority_normalize(pp);
+               }
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               assert((pp & _PTHREAD_PRIORITY_EVENT_MANAGER_FLAG) == 0);
+               pp = _pthread_priority_normalize(pp);
+       } else {
+               pp = _pthread_unspecified_priority();
+               qos = THREAD_QOS_UNSPECIFIED;
+       }
 
-       /* always set requested */
-       kn->kn_req_index = qos_index;
+       kn->kn_qos = pp;
+       kn->kn_req_index = qos;
+
+       if ((kn->kn_status & KN_MERGE_QOS) == 0 || qos > kn->kn_qos_override) {
+               /* Never lower QoS when in "Merge" mode */
+               kn->kn_qos_override = qos;
+       }
 
        /* only adjust in-use qos index when not suppressed */
-       if ((kn->kn_status & KN_SUPPRESSED) == 0)
-               kn->kn_qos_index = qos_index;
+       if ((kn->kn_status & KN_SUPPRESSED) == 0) {
+               kn->kn_qos_index = qos;
+       } else if (kq->kq_state & KQ_WORKQ) {
+               kqworkq_update_override((struct kqworkq *)kq, kn, qos);
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               kqworkloop_update_override((struct kqworkloop *)kq, qos);
+       }
+}
+
+static void
+knote_set_qos_overcommit(struct knote *kn)
+{
+       struct kqueue *kq = knote_get_kq(kn);
+
+       /* turn overcommit on for the appropriate thread request? */
+       if ((kn->kn_qos & _PTHREAD_PRIORITY_OVERCOMMIT_FLAG) &&
+                       (kq->kq_state & KQ_WORKLOOP)) {
+               struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+               struct kqrequest *kqr = &kqwl->kqwl_request;
+
+               /*
+                * This test is racy, but since we never remove this bit,
+                * it allows us to avoid taking a lock.
+                */
+               if (kqr->kqr_state & KQR_THOVERCOMMIT) {
+                       return;
+               }
+
+               kq_req_lock(kqwl);
+               kqr->kqr_state |= KQR_THOVERCOMMIT;
+               if (!kqr->kqr_thread && (kqr->kqr_state & KQR_THREQUESTED)) {
+                       kqueue_threadreq_modify(kq, kqr, kqr->kqr_req.tr_qos);
+               }
+               kq_req_unlock(kqwl);
+       }
 }
 
 static kq_index_t
@@ -4133,215 +6660,285 @@ knote_get_qos_override_index(struct knote *kn)
 }
 
 static void
-knote_set_qos_override_index(struct knote *kn, kq_index_t override_index)
+kqworkq_update_override(struct kqworkq *kqwq, struct knote *kn,
+               kq_index_t override_index)
 {
-       struct kqueue *kq = knote_get_kq(kn);
-       kq_index_t qos_index = knote_get_qos_index(kn);
+       struct kqrequest *kqr;
+       kq_index_t old_override_index;
+       kq_index_t queue_index = kn->kn_qos_index;
 
-       assert((kn->kn_status & KN_QUEUED) == 0);
+       if (override_index <= queue_index) {
+               return;
+       }
 
-       if (override_index == KQWQ_QOS_MANAGER)
-               assert(qos_index == KQWQ_QOS_MANAGER);
-       else 
-               assert(override_index < KQWQ_QOS_MANAGER);
+       kqr = kqworkq_get_request(kqwq, queue_index);
 
-       kn->kn_qos_override = override_index;
+       kq_req_lock(kqwq);
+       old_override_index = kqr->kqr_override_index;
+       if (override_index > MAX(kqr->kqr_qos_index, old_override_index)) {
+               kqr->kqr_override_index = override_index;
 
-       /* 
-        * If this is a workq kqueue, apply the override to the 
-        * workq servicing thread.  
-        */
-       if (kq->kq_state & KQ_WORKQ)  {
-               struct kqworkq *kqwq = (struct kqworkq *)kq;
+               /* apply the override to [incoming?] servicing thread */
+               if (kqr->kqr_thread) {
+                       if (old_override_index)
+                               thread_update_ipc_override(kqr->kqr_thread, override_index);
+                       else
+                               thread_add_ipc_override(kqr->kqr_thread, override_index);
+               }
+       }
+       kq_req_unlock(kqwq);
+}
+
+static void
+kqworkloop_update_override(struct kqworkloop *kqwl, kq_index_t override_index)
+{
+       kq_req_lock(kqwl);
+       kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_UPDATE_WAKEUP_OVERRIDE,
+                       override_index);
+       kq_req_unlock(kqwl);
+}
+
+static thread_qos_t
+kqworkloop_unbind_locked(struct kqworkloop *kqwl, thread_t thread)
+{
+       struct uthread *ut = get_bsdthread_info(thread);
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       kq_index_t ipc_override = ut->uu_kqueue_override;
+
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWL_UNBIND), kqwl->kqwl_dynamicid,
+                       thread_tid(thread), 0, 0);
 
-               assert(qos_index > QOS_INDEX_KQFILE);
-               kqworkq_update_override(kqwq, qos_index, override_index);
+       kq_req_held(kqwl);
+       assert(ut->uu_kqr_bound == kqr);
+       ut->uu_kqr_bound = NULL;
+       ut->uu_kqueue_override = THREAD_QOS_UNSPECIFIED;
+
+       if (kqwl->kqwl_owner == NULL && kqwl->kqwl_turnstile) {
+               turnstile_update_inheritor(kqwl->kqwl_turnstile,
+                               TURNSTILE_INHERITOR_NULL, TURNSTILE_IMMEDIATE_UPDATE);
+               turnstile_update_inheritor_complete(kqwl->kqwl_turnstile,
+                               TURNSTILE_INTERLOCK_HELD);
        }
+
+       kqr->kqr_thread = NULL;
+       kqr->kqr_state &= ~(KQR_THREQUESTED | KQR_R2K_NOTIF_ARMED);
+       return ipc_override;
 }
 
+/*
+ *     kqworkloop_unbind - Unbind the servicer thread of a workloop kqueue
+ *
+ *     It will acknowledge events, and possibly request a new thread if:
+ *     - there were active events left
+ *     - we pended waitq hook callouts during processing
+ *     - we pended wakeups while processing (or unsuppressing)
+ *
+ *     Called with kqueue lock held.
+ */
 static void
-kqworkq_update_override(struct kqworkq *kqwq, kq_index_t qos_index, kq_index_t override_index)
+kqworkloop_unbind(proc_t p, struct kqworkloop *kqwl)
 {
-       struct kqrequest *kqr;
-       kq_index_t new_delta;
-       kq_index_t old_delta;
+       struct kqueue *kq = &kqwl->kqwl_kqueue;
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       thread_t thread = kqr->kqr_thread;
+       int op = KQWL_UTQ_PARKING;
+       kq_index_t ipc_override, qos_override = THREAD_QOS_UNSPECIFIED;
 
-       new_delta = (override_index > qos_index) ?
-                   override_index - qos_index : 0;
+       assert(thread == current_thread());
 
-       kqr = kqworkq_get_request(kqwq, qos_index);
+       kqlock(kqwl);
+
+       /*
+        * Forcing the KQ_PROCESSING flag allows for QoS updates because of
+        * unsuppressing knotes not to be applied until the eventual call to
+        * kqworkloop_update_threads_qos() below.
+        */
+       assert((kq->kq_state & KQ_PROCESSING) == 0);
+       if (!TAILQ_EMPTY(&kqr->kqr_suppressed)) {
+               kq->kq_state |= KQ_PROCESSING;
+               qos_override = kqworkloop_acknowledge_events(kqwl);
+               kq->kq_state &= ~KQ_PROCESSING;
+       }
 
-       kqwq_req_lock(kqwq);
-       old_delta = kqr->kqr_override_delta;
+       kq_req_lock(kqwl);
 
-       if (new_delta > old_delta) {
-               thread_t wqthread = kqr->kqr_thread;
+       ipc_override = kqworkloop_unbind_locked(kqwl, thread);
+       kqworkloop_update_threads_qos(kqwl, op, qos_override);
 
-               /* store the new override delta */
-               kqr->kqr_override_delta = new_delta;
+       kq_req_unlock(kqwl);
 
-               /* apply the override to [incoming?] servicing thread */
-               if (wqthread) {
-                       /* only apply if non-manager */
-                   if ((kqr->kqr_state & KQWQ_THMANAGER) == 0) {
-                               if (old_delta)
-                                       thread_update_ipc_override(wqthread, override_index);
-                               else
-                                       thread_add_ipc_override(wqthread, override_index);
-                       }
-               }
+       kqunlock(kqwl);
+
+       /*
+        * Drop the override on the current thread last, after the call to
+        * kqworkloop_update_threads_qos above.
+        */
+       if (ipc_override) {
+               thread_drop_ipc_override(thread);
        }
-       kqwq_req_unlock(kqwq);
+
+       /* If last reference, dealloc the workloop kq */
+       kqueue_release_last(p, kqwl);
+}
+
+static thread_qos_t
+kqworkq_unbind_locked(__assert_only struct kqworkq *kqwq,
+               struct kqrequest *kqr, thread_t thread)
+{
+       struct uthread *ut = get_bsdthread_info(thread);
+       kq_index_t old_override = kqr->kqr_override_index;
+
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KQWQ_UNBIND), -1,
+                       thread_tid(kqr->kqr_thread), kqr->kqr_qos_index, 0);
+
+       kq_req_held(kqwq);
+       assert(ut->uu_kqr_bound == kqr);
+       ut->uu_kqr_bound = NULL;
+       kqr->kqr_thread = NULL;
+       kqr->kqr_state &= ~(KQR_THREQUESTED | KQR_R2K_NOTIF_ARMED);
+       kqr->kqr_override_index = THREAD_QOS_UNSPECIFIED;
+
+       return old_override;
 }
 
-/* called with the kqworkq lock held */
+/*
+ *     kqworkq_unbind - unbind of a workq kqueue from a thread
+ *
+ *     We may have to request new threads.
+ *     This can happen there are no waiting processing threads and:
+ *     - there were active events we never got to (count > 0)
+ *     - we pended waitq hook callouts during processing
+ *     - we pended wakeups while processing (or unsuppressing)
+ */
 static void
-kqworkq_bind_thread(
-       struct kqworkq *kqwq,
-       kq_index_t qos_index,
-       thread_t thread,
-       unsigned int flags)
+kqworkq_unbind(proc_t p, struct kqrequest *kqr)
 {
-       struct kqrequest *kqr = kqworkq_get_request(kqwq, qos_index);
-       thread_t old_thread = kqr->kqr_thread;
-       struct uthread *ut;
+       struct kqworkq *kqwq = (struct kqworkq *)p->p_fd->fd_wqkqueue;
+       __assert_only int rc;
 
-       assert(kqr->kqr_state & KQWQ_THREQUESTED);
+       kqlock(kqwq);
+       rc = kqworkq_acknowledge_events(kqwq, kqr, 0, KQWQAE_UNBIND);
+       assert(rc == -1);
+       kqunlock(kqwq);
+}
 
-       /* If no identity yet, just set flags as needed */
-       if (thread == THREAD_NULL) {
-               assert(old_thread == THREAD_NULL);
+struct kqrequest *
+kqworkq_get_request(struct kqworkq *kqwq, kq_index_t qos_index)
+{
+       assert(qos_index < KQWQ_NBUCKETS);
+       return &kqwq->kqwq_request[qos_index];
+}
 
-               /* emergency or unindetified */
-               if (flags & KEVENT_FLAG_WORKQ_MANAGER) {
-                       assert((kqr->kqr_state & KQWQ_THMANAGER) == 0);
-                       kqr->kqr_state |= KQWQ_THMANAGER;
-               }
-               return;
-       }
+static void
+knote_apply_qos_override(struct knote *kn, kq_index_t qos_index)
+{
+       assert((kn->kn_status & KN_QUEUED) == 0);
 
-       /* Known thread identity */
-       ut = get_bsdthread_info(thread);
+       kn->kn_qos_override = qos_index;
 
-       /* 
-        * If this is a manager, and the manager request bit is
-        * not set, assure no other thread is bound. If the bit
-        * is set, make sure the old thread is us (or not set).
-        */
-       if (flags & KEVENT_FLAG_WORKQ_MANAGER) {
-               if ((kqr->kqr_state & KQWQ_THMANAGER) == 0) {
-                       assert(old_thread == THREAD_NULL);
-                       kqr->kqr_state |= KQWQ_THMANAGER;
-               } else if (old_thread == THREAD_NULL) {
-                       kqr->kqr_thread = thread;
-                       ut->uu_kqueue_bound = KQWQ_QOS_MANAGER;
-                       ut->uu_kqueue_flags = (KEVENT_FLAG_WORKQ | 
-                                              KEVENT_FLAG_WORKQ_MANAGER);
+       if (kn->kn_status & KN_SUPPRESSED) {
+               struct kqueue *kq = knote_get_kq(kn);
+               /*
+                * For suppressed events, the kn_qos_index field cannot be touched as it
+                * allows us to know on which supress queue the knote is for a kqworkq.
+                *
+                * Also, there's no natural push applied on the kqueues when this field
+                * changes anyway. We hence need to apply manual overrides in this case,
+                * which will be cleared when the events are later acknowledged.
+                */
+               if (kq->kq_state & KQ_WORKQ) {
+                       kqworkq_update_override((struct kqworkq *)kq, kn, qos_index);
                } else {
-                       assert(thread == old_thread);
-                       assert(ut->uu_kqueue_bound == KQWQ_QOS_MANAGER);
-                       assert(ut->uu_kqueue_flags & KEVENT_FLAG_WORKQ_MANAGER);
+                       kqworkloop_update_override((struct kqworkloop *)kq, qos_index);
                }
-               return;
+       } else {
+               kn->kn_qos_index = qos_index;
        }
-
-       /* Just a normal one-queue servicing thread */
-       assert(old_thread == THREAD_NULL);
-       assert((kqr->kqr_state & KQWQ_THMANAGER) == 0);
-
-       kqr->kqr_thread = thread;
-       
-       /* apply an ipc QoS override if one is needed */
-       if (kqr->kqr_override_delta)
-               thread_add_ipc_override(thread, qos_index + kqr->kqr_override_delta);
-
-       /* indicate that we are processing in the uthread */
-       ut->uu_kqueue_bound = qos_index;
-       ut->uu_kqueue_flags = flags;
 }
 
-/* called with the kqworkq lock held */
-static void
-kqworkq_unbind_thread(
-       struct kqworkq *kqwq,
-       kq_index_t qos_index,
-       thread_t thread, 
-       __unused unsigned int flags)
+static bool
+knote_should_apply_qos_override(struct kqueue *kq, struct knote *kn, int result,
+               thread_qos_t *qos_out)
 {
-       struct kqrequest *kqr = kqworkq_get_request(kqwq, qos_index);
-       kq_index_t override = 0;
+       thread_qos_t qos_index = (result >> FILTER_ADJUST_EVENT_QOS_SHIFT) & 7;
 
-       assert(thread == current_thread());
+       kqlock_held(kq);
 
-       /* 
-        * If there is an override, drop it from the current thread
-        * and then we are free to recompute (a potentially lower)
-        * minimum override to apply to the next thread request.
-        */
-       if (kqr->kqr_override_delta) {
-               struct kqtailq *base_queue = kqueue_get_base_queue(&kqwq->kqwq_kqueue, qos_index);
-               struct kqtailq *queue = kqueue_get_high_queue(&kqwq->kqwq_kqueue, qos_index);
+       assert(result & FILTER_ADJUST_EVENT_QOS_BIT);
+       assert(qos_index < THREAD_QOS_LAST);
 
-               /* if not bound to a manager thread, drop the current ipc override */
-               if ((kqr->kqr_state & KQWQ_THMANAGER) == 0) {
-                       assert(thread == kqr->kqr_thread);
-                       thread_drop_ipc_override(thread);
+       /*
+        * Early exit for knotes that should not change QoS
+        *
+        * It is safe to test kn_req_index against MANAGER / STAYACTIVE because
+        * knotes with such kn_req_index values never change for their entire
+        * lifetime.
+        */
+       if (__improbable(!knote_fops(kn)->f_adjusts_qos)) {
+               panic("filter %d cannot change QoS", kn->kn_filtid);
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               if (kn->kn_req_index == KQWL_BUCKET_STAYACTIVE) {
+                       return false;
                }
+       } else if (kq->kq_state & KQ_WORKQ) {
+               if (kn->kn_req_index == KQWQ_QOS_MANAGER) {
+                       return false;
+               }
+       } else {
+               return false;
+       }
 
-               /* recompute the new override */
-               do {
-                       if (!TAILQ_EMPTY(queue)) {
-                               override = queue - base_queue;
-                               break;
-                       }
-               } while (queue-- > base_queue);
+       /*
+        * knotes with the FALLBACK flag will only use their registration QoS if the
+        * incoming event has no QoS, else, the registration QoS acts as a floor.
+        */
+       if (kn->kn_qos & _PTHREAD_PRIORITY_FALLBACK_FLAG) {
+               if (qos_index == THREAD_QOS_UNSPECIFIED)
+                       qos_index = kn->kn_req_index;
+       } else {
+               if (qos_index < kn->kn_req_index)
+                       qos_index = kn->kn_req_index;
+       }
+       if ((kn->kn_status & KN_MERGE_QOS) && (qos_index < kn->kn_qos_override)) {
+               /* Never lower QoS when in "Merge" mode */
+               return false;
        }
 
-       /* unbind the thread and apply the new override */
-       kqr->kqr_thread = THREAD_NULL;
-       kqr->kqr_override_delta = override;
-}
+       if ((kn->kn_status & KN_LOCKED) && kn->kn_inuse) {
+               /*
+                * When we're trying to update the QoS override and that both an
+                * f_event() and other f_* calls are running concurrently, any of these
+                * in flight calls may want to perform overrides that aren't properly
+                * serialized with each other.
+                *
+                * The first update that observes this racy situation enters a "Merge"
+                * mode which causes subsequent override requests to saturate the
+                * override instead of replacing its value.
+                *
+                * This mode is left when knote_unlock() or knote_call_filter_event()
+                * observe that no other f_* routine is in flight.
+                */
+               kn->kn_status |= KN_MERGE_QOS;
+       }
 
-struct kqrequest *
-kqworkq_get_request(struct kqworkq *kqwq, kq_index_t qos_index)
-{
-       assert(qos_index < KQWQ_NQOS);
-       return &kqwq->kqwq_request[qos_index];
+       if (kn->kn_qos_override == qos_index) {
+               return false;
+       }
+
+       *qos_out = qos_index;
+       return true;
 }
 
-void
-knote_adjust_qos(struct knote *kn, qos_t new_qos, qos_t new_override)
-{
-       if (knote_get_kq(kn)->kq_state & KQ_WORKQ) {
-               kq_index_t new_qos_index;
-               kq_index_t new_override_index;
-               kq_index_t servicer_qos_index;
-
-               new_qos_index = qos_index_from_qos(new_qos, FALSE);
-               new_override_index = qos_index_from_qos(new_override, TRUE);
-
-               /* make sure the servicer qos acts as a floor */
-               servicer_qos_index = qos_index_from_qos(kn->kn_qos, FALSE);
-               if (servicer_qos_index > new_qos_index)
-                       new_qos_index = servicer_qos_index;
-               if (servicer_qos_index > new_override_index)
-                       new_override_index = servicer_qos_index;
-
-               kqlock(knote_get_kq(kn));
-               if (new_qos_index != knote_get_req_index(kn) ||
-                   new_override_index != knote_get_qos_override_index(kn)) {
-                       if (kn->kn_status & KN_QUEUED) {
-                               knote_dequeue(kn);
-                               knote_set_qos_index(kn, new_qos_index);
-                               knote_set_qos_override_index(kn, new_override_index);
-                               knote_enqueue(kn);
-                               knote_wakeup(kn);
-                       } else {
-                               knote_set_qos_index(kn, new_qos_index);
-                               knote_set_qos_override_index(kn, new_override_index);
-                       }
+static void
+knote_adjust_qos(struct kqueue *kq, struct knote *kn, int result)
+{
+       thread_qos_t qos;
+       if (knote_should_apply_qos_override(kq, kn, result, &qos)) {
+               knote_dequeue(kn);
+               knote_apply_qos_override(kn, qos);
+               if (knote_enqueue(kn) && (kn->kn_status & KN_ACTIVE)) {
+                       knote_wakeup(kn);
                }
-               kqunlock(knote_get_kq(kn));
        }
 }
 
@@ -4350,13 +6947,22 @@ knote_wakeup(struct knote *kn)
 {
        struct kqueue *kq = knote_get_kq(kn);
 
+       kqlock_held(kq);
+
        if (kq->kq_state & KQ_WORKQ) {
-               /* request a servicing thread */
                struct kqworkq *kqwq = (struct kqworkq *)kq;
-               kq_index_t qos_index = knote_get_qos_index(kn);
 
-               kqworkq_request_help(kqwq, qos_index, KQWQ_WAKEUP);
+               kqworkq_request_help(kqwq, kn->kn_qos_index);
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               struct kqworkloop *kqwl = (struct kqworkloop *)kq;
 
+               /*
+                * kqworkloop_end_processing() will perform the required QoS
+                * computations when it unsets the processing mode.
+                */
+               if (!kqworkloop_is_processing_on_current_thread(kqwl)) {
+                       kqworkloop_request_help(kqwl, kn->kn_qos_index);
+               }
        } else {
                struct kqfile *kqf = (struct kqfile *)kq;
 
@@ -4367,17 +6973,15 @@ knote_wakeup(struct knote *kn)
                /* wakeup a thread waiting on this queue */
                if (kq->kq_state & (KQ_SLEEP | KQ_SEL)) {
                        kq->kq_state &= ~(KQ_SLEEP | KQ_SEL);
-                       waitq_wakeup64_all((struct waitq *)&kq->kq_wqs,
-                                          KQ_EVENT,
-                                          THREAD_AWAKENED,
-                                          WAITQ_ALL_PRIORITIES);
+                       waitq_wakeup64_all((struct waitq *)&kq->kq_wqs, KQ_EVENT,
+                                       THREAD_AWAKENED, WAITQ_ALL_PRIORITIES);
                }
 
                /* wakeup other kqueues/select sets we're inside */
                KNOTE(&kqf->kqf_sel.si_note, 0);
        }
 }
-       
+
 /*
  * Called with the kqueue locked
  */
@@ -4402,8 +7006,8 @@ kqueue_interrupt(struct kqueue *kq)
                assert(kq->kq_state & KQ_PROCESSING);
 
                kq->kq_state &= ~KQ_PROCWAIT;
-               suppressq = kqueue_get_suppressed_queue(kq, QOS_INDEX_KQFILE);
-               (void)waitq_wakeup64_all((struct waitq *)&kq->kq_wqs, 
+               suppressq = kqueue_get_suppressed_queue(kq, NULL);
+               (void)waitq_wakeup64_all((struct waitq *)&kq->kq_wqs,
                                         CAST_EVENT64_T(suppressq),
                                         THREAD_RESTART,
                                         WAITQ_ALL_PRIORITIES);
@@ -4426,10 +7030,17 @@ waitq_set__CALLING_PREPOST_HOOK__(void *kq_hook, void *knote_hook, int qos)
 {
 #pragma unused(knote_hook, qos)
 
-       struct kqworkq *kqwq = (struct kqworkq *)kq_hook;
+       struct kqueue *kq = (struct kqueue *)kq_hook;
+
+       if (kq->kq_state & KQ_WORKQ) {
+               struct kqworkq *kqwq = (struct kqworkq *)kq;
+
+               kqworkq_request_help(kqwq, KQWQ_QOS_MANAGER);
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               struct kqworkloop *kqwl = (struct kqworkloop *)kq;
 
-       assert(kqwq->kqwq_state & KQ_WORKQ);
-       kqworkq_request_help(kqwq, KQWQ_QOS_MANAGER, KQWQ_HOOKCALLED);
+               kqworkloop_request_help(kqwl, KQWL_BUCKET_STAYACTIVE);
+       }
 }
 
 void
@@ -4448,8 +7059,7 @@ klist_init(struct klist *list)
  *     the hint) and not deadlock itself.
  *
  *     The object lock should also hold off pending
- *     detach/drop operations.  But we'll prevent it here
- *     too (by taking a use reference) - just in case.
+ *     detach/drop operations.
  */
 void
 knote(struct klist *list, long hint)
@@ -4458,21 +7068,8 @@ knote(struct klist *list, long hint)
 
        SLIST_FOREACH(kn, list, kn_selnext) {
                struct kqueue *kq = knote_get_kq(kn);
-
                kqlock(kq);
-
-               /* If we can get a use reference - deliver event */
-               if (kqlock2knoteuse(kq, kn)) {
-                       int result;
-
-                       /* call the event with only a use count */
-                       result = knote_fops(kn)->f_event(kn, hint);
-
-                       /* if its not going away and triggered */
-                       if (knoteuse2kqlock(kq, kn, 0) && result)
-                               knote_activate(kn);
-                       /* kq lock held */
-               }
+               knote_call_filter_event(kq, kn, hint);
                kqunlock(kq);
        }
 }
@@ -4523,30 +7120,45 @@ knote_vanish(struct klist *list)
 
        SLIST_FOREACH_SAFE(kn, list, kn_selnext, kn_next) {
                struct kqueue *kq = knote_get_kq(kn);
-               int result;
 
                kqlock(kq);
-               if ((kn->kn_status & KN_DROPPING) == 0) {
-
+               if (kn->kn_status & KN_REQVANISH) {
                        /* If EV_VANISH supported - prepare to deliver one */
-                       if (kn->kn_status & KN_REQVANISH) {
-                               kn->kn_status |= KN_VANISHED;
-                               knote_activate(kn);
-
-                       } else if (kqlock2knoteuse(kq, kn)) {
-                               /* call the event with only a use count */
-                               result = knote_fops(kn)->f_event(kn, NOTE_REVOKE);
-                               
-                               /* if its not going away and triggered */
-                               if (knoteuse2kqlock(kq, kn, 0) && result)
-                                       knote_activate(kn);
-                               /* lock held again */
-                       }
+                       kn->kn_status |= KN_VANISHED;
+                       knote_activate(kn);
+               } else {
+                       knote_call_filter_event(kq, kn, NOTE_REVOKE);
                }
                kqunlock(kq);
        }
 }
 
+/*
+ * Force a lazy allocation of the waitqset link
+ * of the kq_wqs associated with the kn
+ * if it wasn't already allocated.
+ *
+ * This allows knote_link_waitq to never block
+ * if reserved_link is not NULL.
+ */
+void
+knote_link_waitqset_lazy_alloc(struct knote *kn)
+{
+       struct kqueue *kq = knote_get_kq(kn);
+       waitq_set_lazy_init_link(&kq->kq_wqs);
+}
+
+/*
+ * Check if a lazy allocation for the waitqset link
+ * of the kq_wqs is needed.
+ */
+boolean_t
+knote_link_waitqset_should_lazy_alloc(struct knote *kn)
+{
+       struct kqueue *kq = knote_get_kq(kn);
+       return waitq_set_should_lazy_init_link(&kq->kq_wqs);
+}
+
 /*
  * For a given knote, link a provided wait queue directly with the kqueue.
  * Wakeups will happen via recursive wait queue support.  But nothing will move
@@ -4556,7 +7168,8 @@ knote_vanish(struct klist *list)
  * kqueue and knote references are held by caller.
  * waitq locked by caller.
  *
- * caller provides the wait queue link structure.
+ * caller provides the wait queue link structure and insures that the kq->kq_wqs
+ * is linked by previously calling knote_link_waitqset_lazy_alloc.
  */
 int
 knote_link_waitq(struct knote *kn, struct waitq *wq, uint64_t *reserved_link)
@@ -4596,17 +7209,15 @@ knote_unlink_waitq(struct knote *kn, struct waitq *wq)
 /*
  * remove all knotes referencing a specified fd
  *
- * Essentially an inlined knote_remove & knote_drop
- * when we know for sure that the thing is a file
- *
  * Entered with the proc_fd lock already held.
  * It returns the same way, but may drop it temporarily.
  */
 void
-knote_fdclose(struct proc *p, int fd, int force)
+knote_fdclose(struct proc *p, int fd)
 {
        struct klist *list;
        struct knote *kn;
+       KNOTE_LOCK_CTX(knlc);
 
 restart:
        list = &p->p_fd->fd_knlist[fd];
@@ -4624,44 +7235,28 @@ restart:
                 * transition it to vanished mode (or skip over
                 * it if already vanished).
                 */
-               if (!force && (kn->kn_status & KN_REQVANISH)) {
-
-                       if ((kn->kn_status & KN_VANISHED) == 0) {
-                               proc_fdunlock(p);
-
-                               /* get detach reference (also marks vanished) */
-                               if (kqlock2knotedetach(kq, kn)) {
-
-                                       /* detach knote and drop fp use reference */
-                                       knote_fops(kn)->f_detach(kn);
-                                       if (knote_fops(kn)->f_isfd)
-                                               fp_drop(p, kn->kn_id, kn->kn_fp, 0);
-
-                                       /* activate it if it's still in existence */
-                                       if (knoteuse2kqlock(kq, kn, 0)) {
-                                               knote_activate(kn);
-                                       }
-                                       kqunlock(kq);
-                               }
-                               proc_fdlock(p);
-                               goto restart;
-                       } else {
-                               kqunlock(kq);
-                               continue;
-                       }
+               if (kn->kn_status & KN_VANISHED) {
+                       kqunlock(kq);
+                       continue;
                }
 
                proc_fdunlock(p);
+               if (!knote_lock(kq, kn, &knlc, KNOTE_KQ_LOCK_ON_SUCCESS)) {
+                       /* the knote was dropped by someone, nothing to do */
+               } else if (kn->kn_status & KN_REQVANISH) {
+                       kn->kn_status |= KN_VANISHED;
+                       kn->kn_status &= ~KN_ATTACHED;
 
-               /*
-                * Convert the kq lock to a drop ref.
-                * If we get it, go ahead and drop it.
-                * Otherwise, we waited for the blocking
-                * condition to complete. Either way,
-                * we dropped the fdlock so start over.
-                */
-               if (kqlock2knotedrop(kq, kn)) {
-                       knote_drop(kn, p);
+                       kqunlock(kq);
+                       knote_fops(kn)->f_detach(kn);
+                       if (knote_fops(kn)->f_isfd)
+                               fp_drop(p, kn->kn_id, kn->kn_fp, 0);
+                       kqlock(kq);
+
+                       knote_activate(kn);
+                       knote_unlock(kq, kn, &knlc, KNOTE_KQ_UNLOCK);
+               } else {
+                       knote_drop(kq, kn, &knlc);
                }
 
                proc_fdlock(p);
@@ -4669,8 +7264,67 @@ restart:
        }
 }
 
-/* 
- * knote_fdadd - Add knote to the fd table for process
+/*
+ * knote_fdfind - lookup a knote in the fd table for process
+ *
+ * If the filter is file-based, lookup based on fd index.
+ * Otherwise use a hash based on the ident.
+ *
+ * Matching is based on kq, filter, and ident. Optionally,
+ * it may also be based on the udata field in the kevent -
+ * allowing multiple event registration for the file object
+ * per kqueue.
+ *
+ * fd_knhashlock or fdlock held on entry (and exit)
+ */
+static struct knote *
+knote_fdfind(struct kqueue *kq,
+               struct kevent_internal_s *kev,
+               bool is_fd,
+               struct proc *p)
+{
+       struct filedesc *fdp = p->p_fd;
+       struct klist *list = NULL;
+       struct knote *kn = NULL;
+
+       /*
+        * determine where to look for the knote
+        */
+       if (is_fd) {
+               /* fd-based knotes are linked off the fd table */
+               if (kev->ident < (u_int)fdp->fd_knlistsize) {
+                       list = &fdp->fd_knlist[kev->ident];
+               }
+       } else if (fdp->fd_knhashmask != 0) {
+               /* hash non-fd knotes here too */
+               list = &fdp->fd_knhash[KN_HASH((u_long)kev->ident, fdp->fd_knhashmask)];
+       }
+
+       /*
+        * scan the selected list looking for a match
+        */
+       if (list != NULL) {
+               SLIST_FOREACH(kn, list, kn_link) {
+                       if (kq == knote_get_kq(kn) &&
+                           kev->ident == kn->kn_id &&
+                           kev->filter == kn->kn_filter) {
+                               if (kev->flags & EV_UDATA_SPECIFIC) {
+                                       if ((kn->kn_status & KN_UDATA_SPECIFIC) &&
+                                           kev->udata == kn->kn_udata) {
+                                               break; /* matching udata-specific knote */
+                                       }
+                               } else if ((kn->kn_status & KN_UDATA_SPECIFIC) == 0) {
+                                       break; /* matching non-udata-specific knote */
+                               }
+                       }
+               }
+       }
+       return kn;
+}
+
+/*
+ * kq_add_knote- Add knote to the fd table for process
+ * while checking for duplicates.
  *
  * All file-based filters associate a list of knotes by file
  * descriptor index. All other filters hash the knote by ident.
@@ -4678,39 +7332,77 @@ restart:
  * May have to grow the table of knote lists to cover the
  * file descriptor index presented.
  *
- * proc_fdlock held on entry (and exit) 
+ * fd_knhashlock and fdlock unheld on entry (and exit).
+ *
+ * Takes a rwlock boost if inserting the knote is successful.
  */
 static int
-knote_fdadd(struct knote *kn, struct proc *p)
+kq_add_knote(struct kqueue *kq, struct knote *kn, struct knote_lock_ctx *knlc,
+               struct proc *p)
 {
        struct filedesc *fdp = p->p_fd;
        struct klist *list = NULL;
+       int ret = 0;
+       bool is_fd = knote_fops(kn)->f_isfd;
+
+       if (is_fd)
+               proc_fdlock(p);
+       else
+               knhash_lock(p);
+
+       if (knote_fdfind(kq, &kn->kn_kevent, is_fd, p) != NULL) {
+               /* found an existing knote: we can't add this one */
+               ret = ERESTART;
+               goto out_locked;
+       }
+
+       /* knote was not found: add it now */
+       if (!is_fd) {
+               if (fdp->fd_knhashmask == 0) {
+                       u_long size = 0;
+
+                       list = hashinit(CONFIG_KN_HASHSIZE, M_KQUEUE, &size);
+                       if (list == NULL) {
+                               ret = ENOMEM;
+                               goto out_locked;
+                       }
+
+                       fdp->fd_knhash = list;
+                       fdp->fd_knhashmask = size;
+               }
 
-       if (! knote_fops(kn)->f_isfd) {
-               if (fdp->fd_knhashmask == 0)
-                       fdp->fd_knhash = hashinit(CONFIG_KN_HASHSIZE, M_KQUEUE,
-                           &fdp->fd_knhashmask);
                list = &fdp->fd_knhash[KN_HASH(kn->kn_id, fdp->fd_knhashmask)];
+               SLIST_INSERT_HEAD(list, kn, kn_link);
+               ret = 0;
+               goto out_locked;
+
        } else {
+               /* knote is fd based */
+
                if ((u_int)fdp->fd_knlistsize <= kn->kn_id) {
                        u_int size = 0;
 
                        if (kn->kn_id >= (uint64_t)p->p_rlimit[RLIMIT_NOFILE].rlim_cur
-                           || kn->kn_id >= (uint64_t)maxfiles)
-                               return (EINVAL);
-
+                           || kn->kn_id >= (uint64_t)maxfiles) {
+                               ret = EINVAL;
+                               goto out_locked;
+                       }
                        /* have to grow the fd_knlist */
                        size = fdp->fd_knlistsize;
                        while (size <= kn->kn_id)
                                size += KQEXTENT;
 
-                       if (size >= (UINT_MAX/sizeof(struct klist *)))
-                               return (EINVAL);
+                       if (size >= (UINT_MAX/sizeof(struct klist *))) {
+                               ret = EINVAL;
+                               goto out_locked;
+                       }
 
                        MALLOC(list, struct klist *,
                            size * sizeof(struct klist *), M_KQUEUE, M_WAITOK);
-                       if (list == NULL)
-                               return (ENOMEM);
+                       if (list == NULL) {
+                               ret = ENOMEM;
+                               goto out_locked;
+                       }
 
                        bcopy((caddr_t)fdp->fd_knlist, (caddr_t)list,
                            fdp->fd_knlistsize * sizeof(struct klist *));
@@ -4721,144 +7413,141 @@ knote_fdadd(struct knote *kn, struct proc *p)
                        fdp->fd_knlist = list;
                        fdp->fd_knlistsize = size;
                }
+
                list = &fdp->fd_knlist[kn->kn_id];
+               SLIST_INSERT_HEAD(list, kn, kn_link);
+               ret = 0;
+               goto out_locked;
+
        }
-       SLIST_INSERT_HEAD(list, kn, kn_link);
-       return (0);
+
+out_locked:
+       if (ret == 0) {
+               kqlock(kq);
+               assert((kn->kn_status & KN_LOCKED) == 0);
+               (void)knote_lock(kq, kn, knlc, KNOTE_KQ_UNLOCK);
+       }
+       if (is_fd)
+               proc_fdunlock(p);
+       else
+               knhash_unlock(p);
+
+       return ret;
 }
 
-/* 
- * knote_fdremove - remove a knote from the fd table for process
+/*
+ * kq_remove_knote - remove a knote from the fd table for process
  *
  * If the filter is file-based, remove based on fd index.
  * Otherwise remove from the hash based on the ident.
  *
- * proc_fdlock held on entry (and exit)
+ * fd_knhashlock and fdlock unheld on entry (and exit).
  */
 static void
-knote_fdremove(struct knote *kn, struct proc *p)
+kq_remove_knote(struct kqueue *kq, struct knote *kn, struct proc *p,
+               struct knote_lock_ctx *knlc)
 {
        struct filedesc *fdp = p->p_fd;
        struct klist *list = NULL;
+       uint16_t kq_state;
+       bool is_fd;
+
+       is_fd = knote_fops(kn)->f_isfd;
 
-       if (knote_fops(kn)->f_isfd) {
+       if (is_fd)
+               proc_fdlock(p);
+       else
+               knhash_lock(p);
+
+       if (is_fd) {
                assert ((u_int)fdp->fd_knlistsize > kn->kn_id);
                list = &fdp->fd_knlist[kn->kn_id];
        } else {
                list = &fdp->fd_knhash[KN_HASH(kn->kn_id, fdp->fd_knhashmask)];
        }
        SLIST_REMOVE(list, kn, knote, kn_link);
-}
-
-/* 
- * knote_fdfind - lookup a knote in the fd table for process
- *
- * If the filter is file-based, lookup based on fd index.
- * Otherwise use a hash based on the ident.
- *
- * Matching is based on kq, filter, and ident. Optionally,
- * it may also be based on the udata field in the kevent -
- * allowing multiple event registration for the file object
- * per kqueue.
- *
- * proc_fdlock held on entry (and exit)
- */
-static struct knote *
-knote_fdfind(struct kqueue *kq,
-             struct kevent_internal_s *kev,
-             struct proc *p)
-{
-       struct filedesc *fdp = p->p_fd;
-       struct klist *list = NULL;
-       struct knote *kn = NULL;
-       struct filterops *fops;
-       
-       fops = sysfilt_ops[~kev->filter];       /* to 0-base index */
-
-       /* 
-        * determine where to look for the knote
-        */
-       if (fops->f_isfd) {
-               /* fd-based knotes are linked off the fd table */
-               if (kev->ident < (u_int)fdp->fd_knlistsize) {
-                       list = &fdp->fd_knlist[kev->ident];
-               }
-       } else if (fdp->fd_knhashmask != 0) {
-               /* hash non-fd knotes here too */
-               list = &fdp->fd_knhash[KN_HASH((u_long)kev->ident, fdp->fd_knhashmask)];
-       }
 
-       /*
-        * scan the selected list looking for a match
-        */
-       if (list != NULL) {
-               SLIST_FOREACH(kn, list, kn_link) {
-                       if (kq == knote_get_kq(kn) &&
-                           kev->ident == kn->kn_id && 
-                           kev->filter == kn->kn_filter) {
-                               if (kev->flags & EV_UDATA_SPECIFIC) {
-                                       if ((kn->kn_status & KN_UDATA_SPECIFIC) &&
-                                           kev->udata == kn->kn_udata) {
-                                               break; /* matching udata-specific knote */
-                                       }
-                               } else if ((kn->kn_status & KN_UDATA_SPECIFIC) == 0) {
-                                       break; /* matching non-udata-specific knote */
-                               }
-                       }
-               }
+       kqlock(kq);
+       kq_state = kq->kq_state;
+       if (knlc) {
+               knote_unlock_cancel(kq, kn, knlc, KNOTE_KQ_UNLOCK);
+       } else {
+               kqunlock(kq);
        }
-       return kn;
+       if (is_fd)
+               proc_fdunlock(p);
+       else
+               knhash_unlock(p);
+
+       if (kq_state & KQ_DYNAMIC)
+               kqueue_release_last(p, kq);
 }
 
+/*
+ * kq_find_knote_and_kq_lock - lookup a knote in the fd table for process
+ * and, if the knote is found, acquires the kqlock while holding the fd table lock/spinlock.
+ *
+ * fd_knhashlock or fdlock unheld on entry (and exit)
+ */
+
+static struct knote *
+kq_find_knote_and_kq_lock(struct kqueue *kq, struct kevent_internal_s *kev,
+               bool is_fd, struct proc *p)
+{
+       struct knote * ret;
+
+       if (is_fd)
+               proc_fdlock(p);
+       else
+               knhash_lock(p);
+
+       ret = knote_fdfind(kq, kev, is_fd, p);
+
+       if (ret) {
+               kqlock(kq);
+       }
+
+       if (is_fd)
+               proc_fdunlock(p);
+       else
+               knhash_unlock(p);
+
+       return ret;
+}
 /*
  * knote_drop - disconnect and drop the knote
  *
- * Called with the kqueue unlocked and holding a
- * "drop reference" on the knote in question.
- * This reference is most often aquired thru a call
- * to kqlock2knotedrop(). But it can also be acquired
- * through stealing a drop reference via a call to
- * knoteuse2knotedrop() or during the initial attach
- * of the knote.
+ * Called with the kqueue locked, returns with the kqueue unlocked.
+ *
+ * If a knote locking context is passed, it is canceled.
  *
  * The knote may have already been detached from
  * (or not yet attached to) its source object.
  */
 static void
-knote_drop(struct knote *kn, __unused struct proc *ctxp)
+knote_drop(struct kqueue *kq, struct knote *kn, struct knote_lock_ctx *knlc)
 {
-       struct kqueue *kq = knote_get_kq(kn);
        struct proc *p = kq->kq_p;
-       int needswakeup;
 
-       /* We have to have a dropping reference on the knote */
-       assert(kn->kn_status & KN_DROPPING);
+       kqlock_held(kq);
+
+       assert((kn->kn_status & KN_DROPPING) == 0);
+       if (knlc == NULL) {
+               assert((kn->kn_status & KN_LOCKED) == 0);
+       }
+       kn->kn_status |= KN_DROPPING;
+
+       knote_unsuppress(kn);
+       knote_dequeue(kn);
+       knote_wait_for_filter_events(kq, kn);
 
        /* If we are attached, disconnect from the source first */
        if (kn->kn_status & KN_ATTACHED) {
                knote_fops(kn)->f_detach(kn);
        }
 
-       proc_fdlock(p);
-
-       /* Remove the source from the appropriate hash */
-       knote_fdremove(kn, p);
-
-       /* trade fdlock for kq lock */
-       kqlock(kq);
-       proc_fdunlock(p);
-
-       /* determine if anyone needs to know about the drop */
-       assert((kn->kn_status & (KN_SUPPRESSED | KN_QUEUED)) == 0);
-       needswakeup = (kn->kn_status & KN_USEWAIT);
-       kqunlock(kq);
-
-       if (needswakeup)
-               waitq_wakeup64_all((struct waitq *)&kq->kq_wqs,
-                                  CAST_EVENT64_T(&kn->kn_status),
-                                  THREAD_RESTART,
-                                  WAITQ_ALL_PRIORITIES);
-
+       /* kq may be freed when kq_remove_knote() returns */
+       kq_remove_knote(kq, kn, p, knlc);
        if (knote_fops(kn)->f_isfd && ((kn->kn_status & KN_VANISHED) == 0))
                fp_drop(p, kn->kn_id, kn->kn_fp, 0);
 
@@ -4872,6 +7561,10 @@ knote_activate(struct knote *kn)
        if (kn->kn_status & KN_ACTIVE)
                return;
 
+       KDBG_FILTERED(KEV_EVTID(BSD_KEVENT_KNOTE_ACTIVATE),
+                     kn->kn_udata, kn->kn_status | (kn->kn_id << 32),
+                     kn->kn_filtid);
+
        kn->kn_status |= KN_ACTIVE;
        if (knote_enqueue(kn))
                knote_wakeup(kn);
@@ -4894,8 +7587,29 @@ knote_enable(struct knote *kn)
                return;
 
        kn->kn_status &= ~KN_DISABLED;
-       if (knote_enqueue(kn))
+
+       if (kn->kn_status & KN_SUPPRESSED) {
+               /*
+                * it is possible for userland to have knotes registered for a given
+                * workloop `wl_orig` but really handled on another workloop `wl_new`.
+                *
+                * In that case, rearming will happen from the servicer thread of
+                * `wl_new` which if `wl_orig` is no longer being serviced, would cause
+                * this knote to stay suppressed forever if we only relied on
+                * kqworkloop_acknowledge_events to be called by `wl_orig`.
+                *
+                * However if we see the KQ_PROCESSING bit on `wl_orig` set, we can't
+                * unsuppress because that would mess with the processing phase of
+                * `wl_orig`, however it also means kqworkloop_acknowledge_events()
+                * will be called.
+                */
+               struct kqueue *kq = knote_get_kq(kn);
+               if ((kq->kq_state & KQ_PROCESSING) == 0) {
+                       knote_unsuppress(kn);
+               }
+       } else if (knote_enqueue(kn)) {
                knote_wakeup(kn);
+       }
 }
 
 /* called with kqueue lock held */
@@ -4914,13 +7628,16 @@ static void
 knote_suppress(struct knote *kn)
 {
        struct kqtailq *suppressq;
+       struct kqueue *kq = knote_get_kq(kn);
+
+       kqlock_held(kq);
 
        if (kn->kn_status & KN_SUPPRESSED)
                return;
 
        knote_dequeue(kn);
        kn->kn_status |= KN_SUPPRESSED;
-       suppressq = knote_get_suppressed_queue(kn);
+       suppressq = kqueue_get_suppressed_queue(kq, kn);
        TAILQ_INSERT_TAIL(suppressq, kn, kn_tqe);
 }
 
@@ -4929,21 +7646,46 @@ static void
 knote_unsuppress(struct knote *kn)
 {
        struct kqtailq *suppressq;
+       struct kqueue *kq = knote_get_kq(kn);
+
+       kqlock_held(kq);
 
        if ((kn->kn_status & KN_SUPPRESSED) == 0)
                return;
 
        kn->kn_status &= ~KN_SUPPRESSED;
-       suppressq = knote_get_suppressed_queue(kn);
+       suppressq = kqueue_get_suppressed_queue(kq, kn);
        TAILQ_REMOVE(suppressq, kn, kn_tqe);
 
-       /* udate in-use qos to equal requested qos */
-       kn->kn_qos_index = kn->kn_req_index;
+       /*
+        * If the knote is no longer active, reset its push,
+        * and resynchronize kn_qos_index with kn_qos_override
+        */
+       if ((kn->kn_status & KN_ACTIVE) == 0) {
+               kn->kn_qos_override = kn->kn_req_index;
+       }
+       kn->kn_qos_index = kn->kn_qos_override;
 
        /* don't wakeup if unsuppressing just a stay-active knote */
-       if (knote_enqueue(kn) &&
-           (kn->kn_status & KN_ACTIVE))
+       if (knote_enqueue(kn) && (kn->kn_status & KN_ACTIVE)) {
                knote_wakeup(kn);
+       }
+
+       if ((kq->kq_state & KQ_WORKLOOP) && TAILQ_EMPTY(suppressq)) {
+               struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+
+               if (kqworkloop_is_processing_on_current_thread(kqwl)) {
+                       /*
+                        * kqworkloop_end_processing() or kqworkloop_begin_processing()
+                        * will perform the required QoS computations when it unsets the
+                        * processing mode.
+                        */
+               } else {
+                       kq_req_lock(kqwl);
+                       kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_RESET_WAKEUP_OVERRIDE, 0);
+                       kq_req_unlock(kqwl);
+               }
+       }
 }
 
 /* called with kqueue lock held */
@@ -4958,6 +7700,7 @@ knote_enqueue(struct knote *kn)
                struct kqtailq *queue = knote_get_queue(kn);
                struct kqueue *kq = knote_get_kq(kn);
 
+               kqlock_held(kq);
                TAILQ_INSERT_TAIL(queue, kn, kn_tqe);
                kn->kn_status |= KN_QUEUED;
                kq->kq_count++;
@@ -4974,6 +7717,8 @@ knote_dequeue(struct knote *kn)
        struct kqueue *kq = knote_get_kq(kn);
        struct kqtailq *queue;
 
+       kqlock_held(kq);
+
        if ((kn->kn_status & KN_QUEUED) == 0)
                return;
 
@@ -4995,6 +7740,9 @@ knote_init(void)
        kqworkq_zone = zinit(sizeof(struct kqworkq), 8192*sizeof(struct kqworkq),
                            8192, "kqueue workq zone");
 
+       kqworkloop_zone = zinit(sizeof(struct kqworkloop), 8192*sizeof(struct kqworkloop),
+                           8192, "kqueue workloop zone");
+
        /* allocate kq lock group attribute and group */
        kq_lck_grp_attr = lck_grp_attr_alloc_init();
 
@@ -5003,12 +7751,6 @@ knote_init(void)
        /* Allocate kq lock attribute */
        kq_lck_attr = lck_attr_alloc_init();
 
-       /* Initialize the timer filter lock */
-       lck_mtx_init(&_filt_timerlock, kq_lck_grp, kq_lck_attr);
-
-       /* Initialize the user filter lock */
-       lck_spin_init(&_filt_userlock, kq_lck_grp, kq_lck_attr);
-
 #if CONFIG_MEMORYSTATUS
        /* Initialize the memorystatus list lock */
        memorystatus_kevent_init(kq_lck_grp, kq_lck_attr);
@@ -5016,7 +7758,7 @@ knote_init(void)
 }
 SYSINIT(knote, SI_SUB_PSEUDO, SI_ORDER_ANY, knote_init, NULL)
 
-struct filterops *
+const struct filterops *
 knote_fops(struct knote *kn)
 {
        return sysfilt_ops[kn->kn_filtid];
@@ -5025,12 +7767,16 @@ knote_fops(struct knote *kn)
 static struct knote *
 knote_alloc(void)
 {
-       return ((struct knote *)zalloc(knote_zone));
+       struct knote *kn = ((struct knote *)zalloc(knote_zone));
+       bzero(kn, sizeof(struct knote));
+       return kn;
 }
 
 static void
 knote_free(struct knote *kn)
 {
+       assert(kn->kn_inuse == 0);
+       assert((kn->kn_status & KN_LOCKED) == 0);
        zfree(knote_zone, kn);
 }
 
@@ -5062,7 +7808,7 @@ static lck_rw_t *kev_rwlock = &kev_lck_data;
 static int kev_attach(struct socket *so, int proto, struct proc *p);
 static int kev_detach(struct socket *so);
 static int kev_control(struct socket *so, u_long cmd, caddr_t data,
-    struct ifnet *ifp, struct proc *p);
+               struct ifnet *ifp, struct proc *p);
 static lck_mtx_t * event_getlock(struct socket *, int);
 static int event_lock(struct socket *, int, void *);
 static int event_unlock(struct socket *, int, void *);
@@ -5097,17 +7843,17 @@ SYSCTL_NODE(_net_systm, OID_AUTO, kevt,
 
 struct kevtstat kevtstat;
 SYSCTL_PROC(_net_systm_kevt, OID_AUTO, stats,
-    CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_LOCKED, 0, 0,
-    kevt_getstat, "S,kevtstat", "");
+               CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_LOCKED, 0, 0,
+               kevt_getstat, "S,kevtstat", "");
 
 SYSCTL_PROC(_net_systm_kevt, OID_AUTO, pcblist,
        CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_LOCKED, 0, 0,
        kevt_pcblist, "S,xkevtpcb", "");
 
 static lck_mtx_t *
-event_getlock(struct socket *so, int locktype)
+event_getlock(struct socket *so, int flags)
 {
-#pragma unused(locktype)
+#pragma unused(flags)
        struct kern_event_pcb *ev_pcb = (struct kern_event_pcb *)so->so_pcb;
 
        if (so->so_pcb != NULL)  {
@@ -5167,9 +7913,9 @@ event_unlock(struct socket *so, int refcount, void *lr)
        else
                lr_saved = lr;
 
-       if (refcount)
+       if (refcount) {
                so->so_usecount--;
-
+       }
        if (so->so_usecount < 0) {
                panic("%s: so=%p usecount=%d lrh= %s\n", __func__,
                    so, so->so_usecount, solockhistory_nr(so));
@@ -5183,7 +7929,7 @@ event_unlock(struct socket *so, int refcount, void *lr)
        }
        mutex_held = (&((struct kern_event_pcb *)so->so_pcb)->evp_mtx);
 
-       lck_mtx_assert(mutex_held, LCK_MTX_ASSERT_OWNED);
+       LCK_MTX_ASSERT(mutex_held, LCK_MTX_ASSERT_OWNED);
        so->unlock_lr[so->next_unlock_lr] = lr_saved;
        so->next_unlock_lr = (so->next_unlock_lr+1) % SO_LCKDBG_MAX;
 
@@ -5202,7 +7948,7 @@ event_sofreelastref(struct socket *so)
 {
        struct kern_event_pcb *ev_pcb = (struct kern_event_pcb *)so->so_pcb;
 
-       lck_mtx_assert(&(ev_pcb->evp_mtx), LCK_MTX_ASSERT_OWNED);
+       LCK_MTX_ASSERT(&(ev_pcb->evp_mtx), LCK_MTX_ASSERT_OWNED);
 
        so->so_pcb = NULL;
 
@@ -5216,7 +7962,7 @@ event_sofreelastref(struct socket *so)
        so->so_event = sonullevent;
        lck_mtx_unlock(&(ev_pcb->evp_mtx));
 
-       lck_mtx_assert(&(ev_pcb->evp_mtx), LCK_MTX_ASSERT_NOTOWNED);
+       LCK_MTX_ASSERT(&(ev_pcb->evp_mtx), LCK_MTX_ASSERT_NOTOWNED);
        lck_rw_lock_exclusive(kev_rwlock);
        LIST_REMOVE(ev_pcb, evp_link);
        kevtstat.kes_pcbcount--;
@@ -5345,7 +8091,7 @@ kev_detach(struct socket *so)
  */
 errno_t kev_vendor_code_find(
        const char      *string,
-       u_int32_t       *out_vendor_code)
+       u_int32_t       *out_vendor_code)
 {
        if (strlen(string) >= KEV_VENDOR_CODE_MAX_STR_LEN) {
                return (EINVAL);
@@ -5364,7 +8110,7 @@ kev_msg_post(struct kev_msg *event_msg)
        if (event_msg == NULL)
                return (EINVAL);
 
-       /* 
+       /*
         * Limit third parties to posting events for registered vendor codes
         * only
         */
@@ -5400,7 +8146,7 @@ kev_post_msg(struct kev_msg *event_msg)
                return (EMSGSIZE);
        }
 
-       m = m_get(M_DONTWAIT, MT_DATA);
+       m = m_get(M_WAIT, MT_DATA);
        if (m == 0) {
                OSIncrementAtomic64((SInt64 *)&kevtstat.kes_nomem);
                return (ENOMEM);
@@ -5458,7 +8204,7 @@ kev_post_msg(struct kev_msg *event_msg)
                        }
                }
 
-               m2 = m_copym(m, 0, m->m_len, M_NOWAIT);
+               m2 = m_copym(m, 0, m->m_len, M_WAIT);
                if (m2 == 0) {
                        OSIncrementAtomic64((SInt64 *)&kevtstat.kes_nomem);
                        m_free(m);
@@ -5489,10 +8235,10 @@ kev_post_msg(struct kev_msg *event_msg)
 
 static int
 kev_control(struct socket *so,
-    u_long cmd,
-    caddr_t data,
-    __unused struct ifnet *ifp,
-    __unused struct proc *p)
+               u_long cmd,
+               caddr_t data,
+               __unused struct ifnet *ifp,
+               __unused struct proc *p)
 {
        struct kev_request *kev_req = (struct kev_request *) data;
        struct kern_event_pcb  *ev_pcb;
@@ -5679,27 +8425,102 @@ fill_kqueueinfo(struct kqueue *kq, struct kqueue_info * kinfo)
        else
                st->vst_blksize = sizeof(struct kevent);
        st->vst_mode = S_IFIFO;
+       st->vst_ino = (kq->kq_state & KQ_DYNAMIC) ?
+               ((struct kqworkloop *)kq)->kqwl_dynamicid : 0;
 
        /* flags exported to libproc as PROC_KQUEUE_* (sys/proc_info.h) */
-#define PROC_KQUEUE_MASK (KQ_SEL|KQ_SLEEP|KQ_KEV32|KQ_KEV64|KQ_KEV_QOS)
+#define PROC_KQUEUE_MASK (KQ_SEL|KQ_SLEEP|KQ_KEV32|KQ_KEV64|KQ_KEV_QOS|KQ_WORKQ|KQ_WORKLOOP)
        kinfo->kq_state = kq->kq_state & PROC_KQUEUE_MASK;
 
        return (0);
 }
 
+static int
+fill_kqueue_dyninfo(struct kqueue *kq, struct kqueue_dyninfo *kqdi)
+{
+       struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+       struct kqrequest *kqr = &kqwl->kqwl_request;
+       workq_threadreq_param_t trp = {};
+       int err;
+
+       if ((kq->kq_state & KQ_WORKLOOP) == 0) {
+               return EINVAL;
+       }
+
+       if ((err = fill_kqueueinfo(kq, &kqdi->kqdi_info))) {
+               return err;
+       }
+
+       kq_req_lock(kqwl);
+
+       kqdi->kqdi_servicer = thread_tid(kqr->kqr_thread);
+       kqdi->kqdi_owner = thread_tid(kqwl->kqwl_owner);
+       kqdi->kqdi_request_state = kqr->kqr_state;
+       kqdi->kqdi_async_qos = kqr->kqr_qos_index;
+       kqdi->kqdi_events_qos = kqr->kqr_override_index;
+       kqdi->kqdi_sync_waiters = kqr->kqr_dsync_waiters;
+       kqdi->kqdi_sync_waiter_qos = 0;
+
+       trp.trp_value = kqwl->kqwl_params;
+       if (trp.trp_flags & TRP_PRIORITY)
+               kqdi->kqdi_pri = trp.trp_pri;
+       else
+               kqdi->kqdi_pri = 0;
+
+       if (trp.trp_flags & TRP_POLICY)
+               kqdi->kqdi_pol = trp.trp_pol;
+       else
+               kqdi->kqdi_pol = 0;
+
+       if (trp.trp_flags & TRP_CPUPERCENT)
+               kqdi->kqdi_cpupercent = trp.trp_cpupercent;
+       else
+               kqdi->kqdi_cpupercent = 0;
+
+       kq_req_unlock(kqwl);
+
+       return 0;
+}
+
 
 void
 knote_markstayactive(struct knote *kn)
 {
-       kqlock(knote_get_kq(kn));
+       struct kqueue *kq = knote_get_kq(kn);
+       kq_index_t qos;
+
+       kqlock(kq);
        kn->kn_status |= KN_STAYACTIVE;
 
-       /* handle all stayactive knotes on the manager */
-       if (knote_get_kq(kn)->kq_state & KQ_WORKQ)
-               knote_set_qos_index(kn, KQWQ_QOS_MANAGER);
+       /*
+        * Making a knote stay active is a property of the knote that must be
+        * established before it is fully attached.
+        */
+       assert(kn->kn_status & KN_ATTACHING);
+       assert((kn->kn_status & (KN_QUEUED | KN_SUPPRESSED)) == 0);
+
+       /* handle all stayactive knotes on the (appropriate) manager */
+       if (kq->kq_state & KQ_WORKQ) {
+               qos = KQWQ_QOS_MANAGER;
+       } else if (kq->kq_state & KQ_WORKLOOP) {
+               struct kqworkloop *kqwl = (struct kqworkloop *)kq;
+
+               qos = _pthread_priority_thread_qos(kn->kn_qos);
+               assert(qos && qos < THREAD_QOS_LAST);
+               kq_req_lock(kq);
+               kqworkloop_update_threads_qos(kqwl, KQWL_UTQ_UPDATE_STAYACTIVE_QOS, qos);
+               kq_req_unlock(kq);
+               qos = KQWL_BUCKET_STAYACTIVE;
+       } else {
+               qos = THREAD_QOS_UNSPECIFIED;
+       }
+
+       kn->kn_req_index = qos;
+       kn->kn_qos_override = qos;
+       kn->kn_qos_index = qos;
 
        knote_activate(kn);
-       kqunlock(knote_get_kq(kn));
+       kqunlock(kq);
 }
 
 void
@@ -5715,27 +8536,27 @@ static unsigned long
 kevent_extinfo_emit(struct kqueue *kq, struct knote *kn, struct kevent_extinfo *buf,
                unsigned long buflen, unsigned long nknotes)
 {
-       struct kevent_internal_s *kevp;
        for (; kn; kn = SLIST_NEXT(kn, kn_link)) {
                if (kq == knote_get_kq(kn)) {
                        if (nknotes < buflen) {
                                struct kevent_extinfo *info = &buf[nknotes];
-                               struct kevent_qos_s kevqos;
+                               struct kevent_internal_s *kevp = &kn->kn_kevent;
 
                                kqlock(kq);
-                               kevp = &(kn->kn_kevent);
-
-                               bzero(&kevqos, sizeof(kevqos));
-                               kevqos.ident = kevp->ident;
-                               kevqos.filter = kevp->filter;
-                               kevqos.flags = kevp->flags;
-                               kevqos.fflags = kevp->fflags;
-                               kevqos.data = (int64_t) kevp->data;
-                               kevqos.udata = kevp->udata;
-                               kevqos.ext[0] = kevp->ext[0];
-                               kevqos.ext[1] = kevp->ext[1];
-
-                               memcpy(&info->kqext_kev, &kevqos, sizeof(info->kqext_kev));
+
+                               info->kqext_kev = (struct kevent_qos_s){
+                                       .ident = kevp->ident,
+                                       .filter = kevp->filter,
+                                       .flags = kevp->flags,
+                                       .fflags = kevp->fflags,
+                                       .data = (int64_t)kevp->data,
+                                       .udata = kevp->udata,
+                                       .ext[0] = kevp->ext[0],
+                                       .ext[1] = kevp->ext[1],
+                                       .ext[2] = kevp->ext[2],
+                                       .ext[3] = kevp->ext[3],
+                                       .qos = kn->kn_req_index,
+                               };
                                info->kqext_sdata = kn->kn_sdata;
                                info->kqext_status = kn->kn_status;
                                info->kqext_sfflags = kn->kn_sfflags;
@@ -5751,6 +8572,146 @@ kevent_extinfo_emit(struct kqueue *kq, struct knote *kn, struct kevent_extinfo *
        return nknotes;
 }
 
+int
+kevent_copyout_proc_dynkqids(void *proc, user_addr_t ubuf, uint32_t ubufsize,
+               int32_t *nkqueues_out)
+{
+       proc_t p = (proc_t)proc;
+       struct filedesc *fdp = p->p_fd;
+       unsigned int nkqueues = 0;
+       unsigned long ubuflen = ubufsize / sizeof(kqueue_id_t);
+       size_t buflen, bufsize;
+       kqueue_id_t *kq_ids = NULL;
+       int err = 0;
+
+       assert(p != NULL);
+
+       if (ubuf == USER_ADDR_NULL && ubufsize != 0) {
+               err = EINVAL;
+               goto out;
+       }
+
+       buflen = min(ubuflen, PROC_PIDDYNKQUEUES_MAX);
+
+       if (ubuflen != 0) {
+               if (os_mul_overflow(sizeof(kqueue_id_t), buflen, &bufsize)) {
+                       err = ERANGE;
+                       goto out;
+               }
+               kq_ids = kalloc(bufsize);
+               if (!kq_ids) {
+                       err = ENOMEM;
+                       goto out;
+               }
+               bzero(kq_ids, bufsize);
+       }
+
+       kqhash_lock(p);
+
+       if (fdp->fd_kqhashmask > 0) {
+               for (uint32_t i = 0; i < fdp->fd_kqhashmask + 1; i++) {
+                       struct kqworkloop *kqwl;
+
+                       SLIST_FOREACH(kqwl, &fdp->fd_kqhash[i], kqwl_hashlink) {
+                               /* report the number of kqueues, even if they don't all fit */
+                               if (nkqueues < buflen) {
+                                       kq_ids[nkqueues] = kqwl->kqwl_dynamicid;
+                               }
+                               nkqueues++;
+                       }
+               }
+       }
+
+       kqhash_unlock(p);
+
+       if (kq_ids) {
+               size_t copysize;
+               if (os_mul_overflow(sizeof(kqueue_id_t), min(buflen, nkqueues), &copysize)) {
+                       err = ERANGE;
+                       goto out;
+               }
+
+               assert(ubufsize >= copysize);
+               err = copyout(kq_ids, ubuf, copysize);
+       }
+
+out:
+       if (kq_ids) {
+               kfree(kq_ids, bufsize);
+       }
+
+       if (!err) {
+               *nkqueues_out = (int)min(nkqueues, PROC_PIDDYNKQUEUES_MAX);
+       }
+       return err;
+}
+
+int
+kevent_copyout_dynkqinfo(void *proc, kqueue_id_t kq_id, user_addr_t ubuf,
+               uint32_t ubufsize, int32_t *size_out)
+{
+       proc_t p = (proc_t)proc;
+       struct kqueue *kq;
+       int err = 0;
+       struct kqueue_dyninfo kqdi = { };
+
+       assert(p != NULL);
+
+       if (ubufsize < sizeof(struct kqueue_info)) {
+               return ENOBUFS;
+       }
+
+       kqhash_lock(p);
+       kq = kqueue_hash_lookup(p, kq_id);
+       if (!kq) {
+               kqhash_unlock(p);
+               return ESRCH;
+       }
+       kqueue_retain(kq);
+       kqhash_unlock(p);
+
+       /*
+        * backward compatibility: allow the argument to this call to only be
+        * a struct kqueue_info
+        */
+       if (ubufsize >= sizeof(struct kqueue_dyninfo)) {
+               ubufsize = sizeof(struct kqueue_dyninfo);
+               err = fill_kqueue_dyninfo(kq, &kqdi);
+       } else {
+               ubufsize = sizeof(struct kqueue_info);
+               err = fill_kqueueinfo(kq, &kqdi.kqdi_info);
+       }
+       if (err == 0 && (err = copyout(&kqdi, ubuf, ubufsize)) == 0) {
+               *size_out = ubufsize;
+       }
+       kqueue_release_last(p, kq);
+       return err;
+}
+
+int
+kevent_copyout_dynkqextinfo(void *proc, kqueue_id_t kq_id, user_addr_t ubuf,
+               uint32_t ubufsize, int32_t *nknotes_out)
+{
+       proc_t p = (proc_t)proc;
+       struct kqueue *kq;
+       int err;
+
+       assert(p != NULL);
+
+       kqhash_lock(p);
+       kq = kqueue_hash_lookup(p, kq_id);
+       if (!kq) {
+               kqhash_unlock(p);
+               return ESRCH;
+       }
+       kqueue_retain(kq);
+       kqhash_unlock(p);
+
+       err = pid_kqueue_extinfo(p, kq, ubuf, ubufsize, nknotes_out);
+       kqueue_release_last(p, kq);
+       return err;
+}
+
 int
 pid_kqueue_extinfo(proc_t p, struct kqueue *kq, user_addr_t ubuf,
                uint32_t bufsize, int32_t *retval)
@@ -5774,25 +8735,25 @@ pid_kqueue_extinfo(proc_t p, struct kqueue *kq, user_addr_t ubuf,
        bzero(kqext, buflen * sizeof(struct kevent_extinfo));
 
        proc_fdlock(p);
-
        for (i = 0; i < fdp->fd_knlistsize; i++) {
                kn = SLIST_FIRST(&fdp->fd_knlist[i]);
                nknotes = kevent_extinfo_emit(kq, kn, kqext, buflen, nknotes);
        }
+       proc_fdunlock(p);
 
        if (fdp->fd_knhashmask != 0) {
                for (i = 0; i < (int)fdp->fd_knhashmask + 1; i++) {
+                       kqhash_lock(p);
                        kn = SLIST_FIRST(&fdp->fd_knhash[i]);
                        nknotes = kevent_extinfo_emit(kq, kn, kqext, buflen, nknotes);
+                       kqhash_unlock(p);
                }
        }
 
-       proc_fdunlock(p);
-
        assert(bufsize >= sizeof(struct kevent_extinfo) * min(buflen, nknotes));
        err = copyout(kqext, ubuf, sizeof(struct kevent_extinfo) * min(buflen, nknotes));
 
- out:
+out:
        if (kqext) {
                kfree(kqext, buflen * sizeof(struct kevent_extinfo));
                kqext = NULL;
@@ -5804,53 +8765,171 @@ pid_kqueue_extinfo(proc_t p, struct kqueue *kq, user_addr_t ubuf,
        return err;
 }
 
-static unsigned long
-kevent_udatainfo_emit(struct kqueue *kq, struct knote *kn, uint64_t *buf,
-               unsigned long buflen, unsigned long nknotes)
+static unsigned int
+klist_copy_udata(struct klist *list, uint64_t *buf,
+               unsigned int buflen, unsigned int nknotes)
 {
-       struct kevent_internal_s *kevp;
-       for (; kn; kn = SLIST_NEXT(kn, kn_link)) {
-               if (kq == knote_get_kq(kn)) {
-                       if (nknotes < buflen) {
-                               kqlock(kq);
-                               kevp = &(kn->kn_kevent);
-                               buf[nknotes] = kevp->udata;
-                               kqunlock(kq);
-                       }
-
-                       /* we return total number of knotes, which may be more than requested */
-                       nknotes++;
+       struct kevent_internal_s *kev;
+       struct knote *kn;
+       SLIST_FOREACH(kn, list, kn_link) {
+               if (nknotes < buflen) {
+                       struct kqueue *kq = knote_get_kq(kn);
+                       kqlock(kq);
+                       kev = &(kn->kn_kevent);
+                       buf[nknotes] = kev->udata;
+                       kqunlock(kq);
                }
+               /* we return total number of knotes, which may be more than requested */
+               nknotes++;
        }
 
        return nknotes;
 }
 
+static unsigned int
+kqlist_copy_dynamicids(__assert_only proc_t p, struct kqlist *list,
+               uint64_t *buf, unsigned int buflen, unsigned int nids)
+{
+       kqhash_lock_held(p);
+       struct kqworkloop *kqwl;
+       SLIST_FOREACH(kqwl, list, kqwl_hashlink) {
+               if (nids < buflen) {
+                       buf[nids] = kqwl->kqwl_dynamicid;
+               }
+               nids++;
+       }
+       return nids;
+}
+
 int
-pid_kqueue_udatainfo(proc_t p, struct kqueue *kq, uint64_t *buf,
-               uint32_t bufsize)
+kevent_proc_copy_uptrs(void *proc, uint64_t *buf, int bufsize)
 {
-       struct knote *kn;
-       int i;
+       proc_t p = (proc_t)proc;
        struct filedesc *fdp = p->p_fd;
-       unsigned long nknotes = 0;
+       unsigned int nuptrs = 0;
        unsigned long buflen = bufsize / sizeof(uint64_t);
 
+       if (buflen > 0) {
+               assert(buf != NULL);
+       }
+
        proc_fdlock(p);
+       for (int i = 0; i < fdp->fd_knlistsize; i++) {
+               nuptrs = klist_copy_udata(&fdp->fd_knlist[i], buf, buflen, nuptrs);
+       }
+       knhash_lock(p);
+       proc_fdunlock(p);
+       if (fdp->fd_knhashmask != 0) {
+               for (int i = 0; i < (int)fdp->fd_knhashmask + 1; i++) {
+                       nuptrs = klist_copy_udata(&fdp->fd_knhash[i], buf, buflen, nuptrs);
+               }
+       }
+       knhash_unlock(p);
 
-       for (i = 0; i < fdp->fd_knlistsize; i++) {
-               kn = SLIST_FIRST(&fdp->fd_knlist[i]);
-               nknotes = kevent_udatainfo_emit(kq, kn, buf, buflen, nknotes);
+       kqhash_lock(p);
+       if (fdp->fd_kqhashmask != 0) {
+               for (int i = 0; i < (int)fdp->fd_kqhashmask + 1; i++) {
+                       nuptrs = kqlist_copy_dynamicids(p, &fdp->fd_kqhash[i], buf, buflen,
+                                       nuptrs);
+               }
        }
+       kqhash_unlock(p);
 
-       if (fdp->fd_knhashmask != 0) {
-               for (i = 0; i < (int)fdp->fd_knhashmask + 1; i++) {
-                       kn = SLIST_FIRST(&fdp->fd_knhash[i]);
-                       nknotes = kevent_udatainfo_emit(kq, kn, buf, buflen, nknotes);
+       return (int)nuptrs;
+}
+
+static void
+kevent_set_return_to_kernel_user_tsd(proc_t p, thread_t thread)
+{
+       uint64_t ast_addr;
+       bool proc_is_64bit = !!(p->p_flag & P_LP64);
+       size_t user_addr_size = proc_is_64bit ? 8 : 4;
+       uint32_t ast_flags32 = 0;
+       uint64_t ast_flags64 = 0;
+       struct uthread *ut = get_bsdthread_info(thread);
+
+       if (ut->uu_kqr_bound != NULL) {
+               ast_flags64 |= R2K_WORKLOOP_PENDING_EVENTS;
+       }
+
+       if (ast_flags64 == 0) {
+               return;
+       }
+
+       if (!(p->p_flag & P_LP64)) {
+               ast_flags32 = (uint32_t)ast_flags64;
+               assert(ast_flags64 < 0x100000000ull);
+       }
+
+       ast_addr = thread_rettokern_addr(thread);
+       if (ast_addr == 0) {
+               return;
+       }
+
+       if (copyout((proc_is_64bit ? (void *)&ast_flags64 : (void *)&ast_flags32),
+                   (user_addr_t)ast_addr,
+                   user_addr_size) != 0) {
+               printf("pid %d (tid:%llu): copyout of return_to_kernel ast flags failed with "
+                      "ast_addr = %llu\n", p->p_pid, thread_tid(current_thread()), ast_addr);
+       }
+}
+
+void
+kevent_ast(thread_t thread, uint16_t bits)
+{
+       proc_t p = current_proc();
+
+       if (bits & AST_KEVENT_REDRIVE_THREADREQ) {
+               workq_kern_threadreq_redrive(p, WORKQ_THREADREQ_CAN_CREATE_THREADS);
+       }
+       if (bits & AST_KEVENT_RETURN_TO_KERNEL) {
+               kevent_set_return_to_kernel_user_tsd(p, thread);
+       }
+}
+
+#if DEVELOPMENT || DEBUG
+
+#define KEVENT_SYSCTL_BOUND_ID 1
+
+static int
+kevent_sysctl SYSCTL_HANDLER_ARGS
+{
+#pragma unused(oidp, arg2)
+       uintptr_t type = (uintptr_t)arg1;
+       uint64_t bound_id = 0;
+
+       if (type != KEVENT_SYSCTL_BOUND_ID) {
+               return EINVAL;
+       }
+
+       if (req->newptr) {
+               return EINVAL;
+       }
+
+       struct uthread *ut = get_bsdthread_info(current_thread());
+       if (!ut) {
+               return EFAULT;
+       }
+
+       struct kqrequest *kqr = ut->uu_kqr_bound;
+       if (kqr) {
+               if (kqr->kqr_state & KQR_WORKLOOP) {
+                       bound_id = kqr_kqworkloop(kqr)->kqwl_dynamicid;
+               } else {
+                       bound_id = -1;
                }
        }
 
-       proc_fdunlock(p);
-       return (int)nknotes;
+       return sysctl_io_number(req, bound_id, sizeof(bound_id), NULL, NULL);
 }
 
+SYSCTL_NODE(_kern, OID_AUTO, kevent, CTLFLAG_RW | CTLFLAG_LOCKED, 0,
+               "kevent information");
+
+SYSCTL_PROC(_kern_kevent, OID_AUTO, bound_id,
+               CTLTYPE_QUAD | CTLFLAG_RD | CTLFLAG_LOCKED | CTLFLAG_MASKED,
+               (void *)KEVENT_SYSCTL_BOUND_ID,
+               sizeof(kqueue_id_t), kevent_sysctl, "Q",
+               "get the ID of the bound kqueue");
+
+#endif /* DEVELOPMENT || DEBUG */