]> git.saurik.com Git - apple/xnu.git/blobdiff - osfmk/ipc/ipc_port.c
xnu-6153.41.3.tar.gz
[apple/xnu.git] / osfmk / ipc / ipc_port.c
index e8fbd9449aaac567419d578c56ff0b762f080b8e..b8cddf28ae5d75998d6242b1592076b04a510291 100644 (file)
@@ -1,8 +1,8 @@
 /*
- * Copyright (c) 2000-2007 Apple Inc. All rights reserved.
+ * Copyright (c) 2000-2019 Apple Inc. All rights reserved.
  *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
- * 
+ *
  * This file contains Original Code and/or Modifications of Original Code
  * as defined in and that are subject to the Apple Public Source License
  * Version 2.0 (the 'License'). You may not use this file except in
  * unlawful or unlicensed copies of an Apple operating system, or to
  * circumvent, violate, or enable the circumvention or violation of, any
  * terms of an Apple operating system software license agreement.
- * 
+ *
  * Please obtain a copy of the License at
  * http://www.opensource.apple.com/apsl/ and read it before using this file.
- * 
+ *
  * The Original Code and all software distributed under the License are
  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  * Please see the License for the specific language governing rights and
  * limitations under the License.
- * 
+ *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  */
 /*
  * @OSF_FREE_COPYRIGHT@
  */
-/* 
+/*
  * Mach Operating System
  * Copyright (c) 1991,1990,1989 Carnegie Mellon University
  * All Rights Reserved.
- * 
+ *
  * Permission to use, copy, modify and distribute this software and its
  * documentation is hereby granted, provided that both the copyright
  * notice and this permission notice appear in all copies of the
  * software, derivative works or modified versions, and any portions
  * thereof, and that both notices appear in supporting documentation.
- * 
+ *
  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
- * 
+ *
  * Carnegie Mellon requests users of this software to return to
- * 
+ *
  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
  *  School of Computer Science
  *  Carnegie Mellon University
  *  Pittsburgh PA 15213-3890
- * 
+ *
  * any improvements or extensions that they make and grant Carnegie Mellon
  * the rights to redistribute these changes.
  */
@@ -78,6 +78,9 @@
 #include <kern/thread.h>
 #include <kern/misc_protos.h>
 #include <kern/waitq.h>
+#include <kern/policy_internal.h>
+#include <kern/debug.h>
+#include <kern/kcdata.h>
 #include <ipc/ipc_entry.h>
 #include <ipc/ipc_space.h>
 #include <ipc/ipc_object.h>
 #include <ipc/ipc_notify.h>
 #include <ipc/ipc_table.h>
 #include <ipc/ipc_importance.h>
+#include <machine/limits.h>
+#include <kern/turnstile.h>
 
 #include <security/mac_mach_internal.h>
 
 #include <string.h>
 
-decl_lck_spin_data(,   ipc_port_multiple_lock_data)
-ipc_port_timestamp_t   ipc_port_timestamp_data;
+decl_lck_spin_data(, ipc_port_multiple_lock_data);
+ipc_port_timestamp_t    ipc_port_timestamp_data;
 int ipc_portbt;
+extern int prioritize_launch;
+
+#if     MACH_ASSERT
+void    ipc_port_init_debug(
+       ipc_port_t      port,
+       uintptr_t       *callstack,
+       unsigned int    callstack_max);
 
-#if    MACH_ASSERT
-void   ipc_port_init_debug(
-               ipc_port_t      port,
-               uintptr_t       *callstack,
-               unsigned int    callstack_max);
+void    ipc_port_callstack_init_debug(
+       uintptr_t       *callstack,
+       unsigned int    callstack_max);
 
-void   ipc_port_callstack_init_debug(
-               uintptr_t       *callstack,
-               unsigned int    callstack_max);
-       
-#endif /* MACH_ASSERT */
+#endif  /* MACH_ASSERT */
+
+static void
+ipc_port_send_turnstile_recompute_push_locked(
+       ipc_port_t port);
+
+static thread_t
+ipc_port_get_watchport_inheritor(
+       ipc_port_t port);
 
 void
 ipc_port_release(ipc_port_t port)
@@ -149,22 +163,22 @@ ipc_port_timestamp(void)
 #if IMPORTANCE_INHERITANCE
 kern_return_t
 ipc_port_request_alloc(
-       ipc_port_t                      port,
-       mach_port_name_t                name,
-       ipc_port_t                      soright,
-       boolean_t                       send_possible,
-       boolean_t                       immediate,
-       ipc_port_request_index_t        *indexp,
-       boolean_t                       *importantp)
+       ipc_port_t                      port,
+       mach_port_name_t                name,
+       ipc_port_t                      soright,
+       boolean_t                       send_possible,
+       boolean_t                       immediate,
+       ipc_port_request_index_t        *indexp,
+       boolean_t                       *importantp)
 #else
 kern_return_t
 ipc_port_request_alloc(
-       ipc_port_t                      port,
-       mach_port_name_t                name,
-       ipc_port_t                      soright,
-       boolean_t                       send_possible,
-       boolean_t                       immediate,
-       ipc_port_request_index_t        *indexp)
+       ipc_port_t                      port,
+       mach_port_name_t                name,
+       ipc_port_t                      soright,
+       boolean_t                       send_possible,
+       boolean_t                       immediate,
+       ipc_port_request_index_t        *indexp)
 #endif /* IMPORTANCE_INHERITANCE */
 {
        ipc_port_request_t ipr, table;
@@ -175,25 +189,27 @@ ipc_port_request_alloc(
        *importantp = FALSE;
 #endif /* IMPORTANCE_INHERITANCE */
 
-       assert(ip_active(port));
+       require_ip_active(port);
        assert(name != MACH_PORT_NULL);
        assert(soright != IP_NULL);
 
        table = port->ip_requests;
 
-       if (table == IPR_NULL)
+       if (table == IPR_NULL) {
                return KERN_NO_SPACE;
+       }
 
        index = table->ipr_next;
-       if (index == 0)
+       if (index == 0) {
                return KERN_NO_SPACE;
+       }
 
        ipr = &table[index];
        assert(ipr->ipr_name == MACH_PORT_NULL);
 
        table->ipr_next = ipr->ipr_next;
        ipr->ipr_name = name;
-       
+
        if (send_possible) {
                mask |= IPR_SOR_SPREQ_MASK;
                if (immediate) {
@@ -205,7 +221,6 @@ ipc_port_request_alloc(
                                if (port->ip_impdonation != 0 &&
                                    port->ip_spimportant == 0 &&
                                    (task_is_importance_donor(current_task()))) {
-                                       port->ip_spimportant = 1;
                                        *importantp = TRUE;
                                }
 #endif /* IMPORTANCE_INHERTANCE */
@@ -237,26 +252,26 @@ ipc_port_request_alloc(
 
 kern_return_t
 ipc_port_request_grow(
-       ipc_port_t              port,
-       ipc_table_elems_t       target_size)
+       ipc_port_t              port,
+       ipc_table_elems_t       target_size)
 {
        ipc_table_size_t its;
        ipc_port_request_t otable, ntable;
-
-       assert(ip_active(port));
+       require_ip_active(port);
 
        otable = port->ip_requests;
-       if (otable == IPR_NULL)
+       if (otable == IPR_NULL) {
                its = &ipc_table_requests[0];
-       else
+       } else {
                its = otable->ipr_size + 1;
+       }
 
        if (target_size != ITS_SIZE_NONE) {
                if ((otable != IPR_NULL) &&
                    (target_size <= otable->ipr_size->its_size)) {
                        ip_unlock(port);
                        return KERN_SUCCESS;
-               }
+               }
                while ((its->its_size) && (its->its_size < target_size)) {
                        its++;
                }
@@ -285,7 +300,7 @@ ipc_port_request_grow(
         */
 
        if (ip_active(port) && (port->ip_requests == otable) &&
-           ((otable == IPR_NULL) || (otable->ipr_size+1 == its))) {
+           ((otable == IPR_NULL) || (otable->ipr_size + 1 == its))) {
                ipc_table_size_t oits;
                ipc_table_elems_t osize, nsize;
                ipc_port_request_index_t free, i;
@@ -298,8 +313,8 @@ ipc_port_request_grow(
                        free = otable->ipr_next;
 
                        (void) memcpy((void *)(ntable + 1),
-                             (const void *)(otable + 1),
-                             (osize - 1) * sizeof(struct ipc_port_request));
+                           (const void *)(otable + 1),
+                           (osize - 1) * sizeof(struct ipc_port_request));
                } else {
                        osize = 1;
                        oits = 0;
@@ -327,7 +342,7 @@ ipc_port_request_grow(
 
                if (otable != IPR_NULL) {
                        it_requests_free(oits, otable);
-               }
+               }
        } else {
                ip_unlock(port);
                ip_release(port);
@@ -336,7 +351,7 @@ ipc_port_request_grow(
 
        return KERN_SUCCESS;
 }
+
 /*
  *     Routine:        ipc_port_request_sparm
  *     Purpose:
@@ -348,48 +363,47 @@ ipc_port_request_grow(
  *             (or armed with importance in that version).
  */
 
-#if IMPORTANCE_INHERITANCE
-boolean_t
-ipc_port_request_sparm(
-       ipc_port_t                      port,
-       __assert_only mach_port_name_t  name,
-       ipc_port_request_index_t        index,
-       mach_msg_option_t               option)
-#else
 boolean_t
 ipc_port_request_sparm(
-       ipc_port_t                      port,
-       __assert_only mach_port_name_t  name,
-       ipc_port_request_index_t        index)
-#endif /* IMPORTANCE_INHERITANCE */
+       ipc_port_t                      port,
+       __assert_only mach_port_name_t  name,
+       ipc_port_request_index_t        index,
+       mach_msg_option_t       option,
+       mach_msg_priority_t override)
 {
        if (index != IE_REQ_NONE) {
                ipc_port_request_t ipr, table;
 
-               assert(ip_active(port));
-       
+               require_ip_active(port);
+
                table = port->ip_requests;
                assert(table != IPR_NULL);
 
                ipr = &table[index];
                assert(ipr->ipr_name == name);
 
+               /* Is there a valid destination? */
                if (IPR_SOR_SPREQ(ipr->ipr_soright)) {
                        ipr->ipr_soright = IPR_SOR_MAKE(ipr->ipr_soright, IPR_SOR_SPARM_MASK);
                        port->ip_sprequests = 1;
+
+                       if (option & MACH_SEND_OVERRIDE) {
+                               /* apply override to message queue */
+                               ipc_mqueue_override_send(&port->ip_messages, override);
+                       }
+
 #if IMPORTANCE_INHERITANCE
                        if (((option & MACH_SEND_NOIMPORTANCE) == 0) &&
                            (port->ip_impdonation != 0) &&
                            (port->ip_spimportant == 0) &&
                            (((option & MACH_SEND_IMPORTANCE) != 0) ||
-                            (task_is_importance_donor(current_task())))) {
-                               port->ip_spimportant = 1;
+                           (task_is_importance_donor(current_task())))) {
                                return TRUE;
                        }
 #else
                        return TRUE;
 #endif /* IMPORTANCE_INHERITANCE */
-               } 
+               }
        }
        return FALSE;
 }
@@ -404,15 +418,15 @@ ipc_port_request_sparm(
  */
 mach_port_type_t
 ipc_port_request_type(
-       ipc_port_t                      port,
-       __assert_only mach_port_name_t  name,
-       ipc_port_request_index_t        index)
+       ipc_port_t                      port,
+       __assert_only mach_port_name_t  name,
+       ipc_port_request_index_t        index)
 {
        ipc_port_request_t ipr, table;
        mach_port_type_t type = 0;
 
        table = port->ip_requests;
-       assert (table != IPR_NULL);
+       assert(table != IPR_NULL);
 
        assert(index != IE_REQ_NONE);
        ipr = &table[index];
@@ -443,18 +457,18 @@ ipc_port_request_type(
 
 ipc_port_t
 ipc_port_request_cancel(
-       ipc_port_t                      port,
-       __assert_only mach_port_name_t  name,
-       ipc_port_request_index_t        index)
+       ipc_port_t                      port,
+       __assert_only mach_port_name_t  name,
+       ipc_port_request_index_t        index)
 {
        ipc_port_request_t ipr, table;
        ipc_port_t request = IP_NULL;
 
-       assert(ip_active(port));
+       require_ip_active(port);
        table = port->ip_requests;
        assert(table != IPR_NULL);
 
-       assert (index != IE_REQ_NONE);
+       assert(index != IE_REQ_NONE);
        ipr = &table[index];
        assert(ipr->ipr_name == name);
        request = IPR_SOR_PORT(ipr->ipr_soright);
@@ -481,13 +495,12 @@ ipc_port_request_cancel(
 
 void
 ipc_port_pdrequest(
-       ipc_port_t      port,
-       ipc_port_t      notify,
-       ipc_port_t      *previousp)
+       ipc_port_t      port,
+       ipc_port_t      notify,
+       ipc_port_t      *previousp)
 {
        ipc_port_t previous;
-
-       assert(ip_active(port));
+       require_ip_active(port);
 
        previous = port->ip_pdrequest;
        port->ip_pdrequest = notify;
@@ -510,15 +523,14 @@ ipc_port_pdrequest(
 
 void
 ipc_port_nsrequest(
-       ipc_port_t              port,
-       mach_port_mscount_t     sync,
-       ipc_port_t              notify,
-       ipc_port_t              *previousp)
+       ipc_port_t              port,
+       mach_port_mscount_t     sync,
+       ipc_port_t              notify,
+       ipc_port_t              *previousp)
 {
        ipc_port_t previous;
        mach_port_mscount_t mscount;
-
-       assert(ip_active(port));
+       require_ip_active(port);
 
        previous = port->ip_nsrequest;
        mscount = port->ip_mscount;
@@ -540,21 +552,31 @@ ipc_port_nsrequest(
 /*
  *     Routine:        ipc_port_clear_receiver
  *     Purpose:
- *             Prepares a receive right for transmission/destruction.
+ *             Prepares a receive right for transmission/destruction,
+ *             optionally performs mqueue destruction (with port lock held)
+ *
  *     Conditions:
  *             The port is locked and active.
+ *     Returns:
+ *             If should_destroy is TRUE, then the return value indicates
+ *             whether the caller needs to reap kmsg structures that should
+ *             be destroyed (by calling ipc_kmsg_reap_delayed)
+ *
+ *              If should_destroy is FALSE, this always returns FALSE
  */
 
-void
+boolean_t
 ipc_port_clear_receiver(
-       ipc_port_t      port)
+       ipc_port_t      port,
+       boolean_t       should_destroy)
 {
-       spl_t           s;
-
-       assert(ip_active(port));
+       ipc_mqueue_t    mqueue = &port->ip_messages;
+       boolean_t       reap_messages = FALSE;
 
        /*
-        * pull ourselves from any sets.
+        * Pull ourselves out of any sets to which we belong.
+        * We hold the port locked, so even though this acquires and releases
+        * the mqueue lock, we know we won't be added to any other sets.
         */
        if (port->ip_in_pset != 0) {
                ipc_pset_remove_from_all(port);
@@ -563,16 +585,46 @@ ipc_port_clear_receiver(
 
        /*
         * Send anyone waiting on the port's queue directly away.
-        * Also clear the mscount and seqno.
+        * Also clear the mscount, seqno, guard bits
         */
-       s = splsched();
-       imq_lock(&port->ip_messages);
-       ipc_mqueue_changed(&port->ip_messages);
-       ipc_port_set_mscount(port, 0);
-       port->ip_messages.imq_seqno = 0;
+       imq_lock(mqueue);
+       if (port->ip_receiver_name) {
+               ipc_mqueue_changed(port->ip_receiver, mqueue);
+       } else {
+               ipc_mqueue_changed(NULL, mqueue);
+       }
+       port->ip_mscount = 0;
+       mqueue->imq_seqno = 0;
        port->ip_context = port->ip_guarded = port->ip_strict_guard = 0;
+       /*
+        * clear the immovable bit so the port can move back to anyone listening
+        * for the port destroy notification
+        */
+       port->ip_immovable_receive = 0;
+
+       if (should_destroy) {
+               /*
+                * Mark the port and mqueue invalid, preventing further send/receive
+                * operations from succeeding. It's important for this to be
+                * done under the same lock hold as the ipc_mqueue_changed
+                * call to avoid additional threads blocking on an mqueue
+                * that's being destroyed.
+                *
+                * The port active bit needs to be guarded under mqueue lock for
+                * turnstiles
+                */
+               port->ip_object.io_bits &= ~IO_BITS_ACTIVE;
+               port->ip_timestamp = ipc_port_timestamp();
+               reap_messages = ipc_mqueue_destroy_locked(mqueue);
+       } else {
+               /* make port be in limbo */
+               port->ip_receiver_name = MACH_PORT_NULL;
+               port->ip_destination = IP_NULL;
+       }
+
        imq_unlock(&port->ip_messages);
-       splx(s);
+
+       return reap_messages;
 }
 
 /*
@@ -584,9 +636,10 @@ ipc_port_clear_receiver(
 
 void
 ipc_port_init(
-       ipc_port_t              port,
-       ipc_space_t             space,
-       mach_port_name_t        name)
+       ipc_port_t              port,
+       ipc_space_t             space,
+       ipc_port_init_flags_t   flags,
+       mach_port_name_t        name)
 {
        /* port->ip_kobject doesn't have to be initialized */
 
@@ -596,6 +649,10 @@ ipc_port_init(
        port->ip_mscount = 0;
        port->ip_srights = 0;
        port->ip_sorights = 0;
+       if (flags & IPC_PORT_INIT_MAKE_SEND_RIGHT) {
+               port->ip_srights = 1;
+               port->ip_mscount = 1;
+       }
 
        port->ip_nsrequest = IP_NULL;
        port->ip_pdrequest = IP_NULL;
@@ -603,6 +660,7 @@ ipc_port_init(
 
        port->ip_premsg = IKM_NULL;
        port->ip_context = 0;
+       port->ip_reply_context = 0;
 
        port->ip_sprequests  = 0;
        port->ip_spimportant = 0;
@@ -611,12 +669,24 @@ ipc_port_init(
 
        port->ip_guarded      = 0;
        port->ip_strict_guard = 0;
+       port->ip_immovable_receive = 0;
+       port->ip_no_grant    = 0;
+       port->ip_immovable_send = 0;
        port->ip_impcount    = 0;
 
-       port->ip_reserved    = 0;
+       port->ip_specialreply = (flags & IPC_PORT_INIT_SPECIAL_REPLY) != 0;
+       port->ip_sync_link_state = PORT_SYNC_LINK_ANY;
+       port->ip_sync_bootstrap_checkin = 0;
+
+       ipc_special_reply_port_bits_reset(port);
 
-       ipc_mqueue_init(&port->ip_messages,
-                       FALSE /* !set */, NULL /* no reserved link */);
+       port->ip_send_turnstile = TURNSTILE_NULL;
+
+       ipc_mqueue_kind_t kind = IPC_MQUEUE_KIND_NONE;
+       if (flags & IPC_PORT_INIT_MESSAGE_QUEUE) {
+               kind = IPC_MQUEUE_KIND_PORT;
+       }
+       ipc_mqueue_init(&port->ip_messages, kind);
 }
 
 /*
@@ -635,27 +705,34 @@ ipc_port_init(
 
 kern_return_t
 ipc_port_alloc(
-       ipc_space_t             space,
-       mach_port_name_t        *namep,
-       ipc_port_t              *portp)
+       ipc_space_t             space,
+       ipc_port_init_flags_t   flags,
+       mach_port_name_t        *namep,
+       ipc_port_t              *portp)
 {
        ipc_port_t port;
        mach_port_name_t name;
        kern_return_t kr;
+       mach_port_type_t type = MACH_PORT_TYPE_RECEIVE;
+       mach_port_urefs_t urefs = 0;
 
 #if     MACH_ASSERT
        uintptr_t buf[IP_CALLSTACK_MAX];
        ipc_port_callstack_init_debug(&buf[0], IP_CALLSTACK_MAX);
 #endif /* MACH_ASSERT */
-           
-       kr = ipc_object_alloc(space, IOT_PORT,
-                             MACH_PORT_TYPE_RECEIVE, 0,
-                             &name, (ipc_object_t *) &port);
-       if (kr != KERN_SUCCESS)
+
+       if (flags & IPC_PORT_INIT_MAKE_SEND_RIGHT) {
+               type |= MACH_PORT_TYPE_SEND;
+               urefs = 1;
+       }
+       kr = ipc_object_alloc(space, IOT_PORT, type, urefs,
+           &name, (ipc_object_t *) &port);
+       if (kr != KERN_SUCCESS) {
                return kr;
+       }
 
        /* port and space are locked */
-       ipc_port_init(port, space, name);
+       ipc_port_init(port, space, flags, name);
 
 #if     MACH_ASSERT
        ipc_port_init_debug(port, &buf[0], IP_CALLSTACK_MAX);
@@ -686,31 +763,38 @@ ipc_port_alloc(
 
 kern_return_t
 ipc_port_alloc_name(
-       ipc_space_t             space,
-       mach_port_name_t        name,
-       ipc_port_t              *portp)
+       ipc_space_t             space,
+       ipc_port_init_flags_t   flags,
+       mach_port_name_t        name,
+       ipc_port_t              *portp)
 {
        ipc_port_t port;
        kern_return_t kr;
+       mach_port_type_t type = MACH_PORT_TYPE_RECEIVE;
+       mach_port_urefs_t urefs = 0;
 
 #if     MACH_ASSERT
        uintptr_t buf[IP_CALLSTACK_MAX];
        ipc_port_callstack_init_debug(&buf[0], IP_CALLSTACK_MAX);
-#endif /* MACH_ASSERT */       
+#endif /* MACH_ASSERT */
 
-       kr = ipc_object_alloc_name(space, IOT_PORT,
-                                  MACH_PORT_TYPE_RECEIVE, 0,
-                                  name, (ipc_object_t *) &port);
-       if (kr != KERN_SUCCESS)
+       if (flags & IPC_PORT_INIT_MAKE_SEND_RIGHT) {
+               type |= MACH_PORT_TYPE_SEND;
+               urefs = 1;
+       }
+       kr = ipc_object_alloc_name(space, IOT_PORT, type, urefs,
+           name, (ipc_object_t *) &port);
+       if (kr != KERN_SUCCESS) {
                return kr;
+       }
 
        /* port is locked */
 
-       ipc_port_init(port, space, name);
+       ipc_port_init(port, space, flags, name);
 
 #if     MACH_ASSERT
        ipc_port_init_debug(port, &buf[0], IP_CALLSTACK_MAX);
-#endif  /* MACH_ASSERT */      
+#endif  /* MACH_ASSERT */
 
        *portp = port;
 
@@ -718,7 +802,7 @@ ipc_port_alloc_name(
 }
 
 /*
- *     Routine:        ipc_port_spnotify
+ *      Routine:       ipc_port_spnotify
  *     Purpose:
  *             Generate send-possible port notifications.
  *     Conditions:
@@ -726,35 +810,33 @@ ipc_port_alloc_name(
  */
 void
 ipc_port_spnotify(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
        ipc_port_request_index_t index = 0;
        ipc_table_elems_t size = 0;
-#if IMPORTANCE_INHERITANCE
-       boolean_t dropassert = FALSE;
-#endif /* IMPORTANCE_INHERITANCE */
 
        /*
         * If the port has no send-possible request
         * armed, don't bother to lock the port.
         */
-       if (port->ip_sprequests == 0)
+       if (port->ip_sprequests == 0) {
                return;
+       }
 
        ip_lock(port);
-       
+
 #if IMPORTANCE_INHERITANCE
        if (port->ip_spimportant != 0) {
                port->ip_spimportant = 0;
-               if (ipc_port_impcount_delta(port, -1, IP_NULL) == -1) {
-                       dropassert = TRUE;
+               if (ipc_port_importance_delta(port, IPID_OPTION_NORMAL, -1) == TRUE) {
+                       ip_lock(port);
                }
        }
 #endif /* IMPORTANCE_INHERITANCE */
 
        if (port->ip_sprequests == 0) {
                ip_unlock(port);
-               goto out;
+               return;
        }
        port->ip_sprequests = 0;
 
@@ -770,8 +852,9 @@ revalidate:
                 * no need to go beyond table size when first
                 * we entered - those are future notifications.
                 */
-               if (size == 0)
+               if (size == 0) {
                        size = requests->ipr_size->its_size;
+               }
 
                /* no need to backtrack either */
                while (++index < size) {
@@ -793,18 +876,11 @@ revalidate:
                }
        }
        ip_unlock(port);
-out:
-#if IMPORTANCE_INHERITANCE
-       if (dropassert == TRUE && ipc_importance_task_is_any_receiver_type(current_task()->task_imp_base)) {
-               /* drop internal assertion */
-               ipc_importance_task_drop_internal_assertion(current_task()->task_imp_base, 1);
-       }
-#endif /* IMPORTANCE_INHERITANCE */
        return;
 }
 
 /*
- *     Routine:        ipc_port_dnnotify
+ *      Routine:       ipc_port_dnnotify
  *     Purpose:
  *             Generate dead name notifications for
  *             all outstanding dead-name and send-
@@ -816,7 +892,7 @@ out:
  */
 void
 ipc_port_dnnotify(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
        ipc_port_request_t requests = port->ip_requests;
 
@@ -852,12 +928,13 @@ ipc_port_dnnotify(
  */
 
 void
-ipc_port_destroy(
-       ipc_port_t      port)
+ipc_port_destroy(ipc_port_t port)
 {
        ipc_port_t pdrequest, nsrequest;
        ipc_mqueue_t mqueue;
        ipc_kmsg_t kmsg;
+       boolean_t special_reply = port->ip_specialreply;
+       struct task_watchport_elem *watchport_elem = NULL;
 
 #if IMPORTANCE_INHERITANCE
        ipc_importance_task_t release_imp_task = IIT_NULL;
@@ -866,11 +943,12 @@ ipc_port_destroy(
        natural_t assertcnt = 0;
 #endif /* IMPORTANCE_INHERITANCE */
 
-       assert(ip_active(port));
+       require_ip_active(port);
        /* port->ip_receiver_name is garbage */
        /* port->ip_receiver/port->ip_destination is garbage */
-       assert(port->ip_in_pset == 0);
-       assert(port->ip_mscount == 0);
+
+       /* clear any reply-port context */
+       port->ip_reply_context = 0;
 
        /* check for a backup port */
        pdrequest = port->ip_pdrequest;
@@ -887,34 +965,64 @@ ipc_port_destroy(
                /* Otherwise, nothing to drop */
        } else {
                assertcnt = port->ip_impcount;
-               if (pdrequest != IP_NULL)
+               if (pdrequest != IP_NULL) {
                        /* mark in limbo for the journey */
                        port->ip_tempowner = 1;
+               }
        }
 
-       if (top)
+       if (top) {
                self->ith_assertions = assertcnt;
+       }
 #endif /* IMPORTANCE_INHERITANCE */
 
        if (pdrequest != IP_NULL) {
+               /* clear receiver, don't destroy the port */
+               (void)ipc_port_clear_receiver(port, FALSE);
+               assert(port->ip_in_pset == 0);
+               assert(port->ip_mscount == 0);
+
                /* we assume the ref for pdrequest */
                port->ip_pdrequest = IP_NULL;
 
-               /* make port be in limbo */
-               port->ip_receiver_name = MACH_PORT_NULL;
-               port->ip_destination = IP_NULL;
-               ip_unlock(port);
+               imq_lock(&port->ip_messages);
+               watchport_elem = ipc_port_clear_watchport_elem_internal(port);
+               ipc_port_send_turnstile_recompute_push_locked(port);
+               /* mqueue and port unlocked */
+
+               if (special_reply) {
+                       ipc_port_adjust_special_reply_port(port,
+                           IPC_PORT_ADJUST_SR_ALLOW_SYNC_LINKAGE);
+               }
 
+               if (watchport_elem) {
+                       task_watchport_elem_deallocate(watchport_elem);
+                       watchport_elem = NULL;
+               }
                /* consumes our refs for port and pdrequest */
                ipc_notify_port_destroyed(pdrequest, port);
 
                goto drop_assertions;
        }
 
-       /* once port is dead, we don't need to keep it locked */
+       /*
+        * The mach_msg_* paths don't hold a port lock, they only hold a
+        * reference to the port object. If a thread raced us and is now
+        * blocked waiting for message reception on this mqueue (or waiting
+        * for ipc_mqueue_full), it will never be woken up. We call
+        * ipc_port_clear_receiver() here, _after_ the port has been marked
+        * inactive, to wakeup any threads which may be blocked and ensure
+        * that no other thread can get lost waiting for a wake up on a
+        * port/mqueue that's been destroyed.
+        */
+       boolean_t reap_msgs = FALSE;
+       reap_msgs = ipc_port_clear_receiver(port, TRUE); /* marks port and mqueue inactive */
+       assert(port->ip_in_pset == 0);
+       assert(port->ip_mscount == 0);
 
-       port->ip_object.io_bits &= ~IO_BITS_ACTIVE;
-       port->ip_timestamp = ipc_port_timestamp();
+       imq_lock(&port->ip_messages);
+       watchport_elem = ipc_port_clear_watchport_elem_internal(port);
+       imq_unlock(&port->ip_messages);
        nsrequest = port->ip_nsrequest;
 
        /*
@@ -922,6 +1030,8 @@ ipc_port_destroy(
         * is not inuse, free it.  If it has an inuse one, then the kmsg
         * free will detect that we freed the association and it can free it
         * like a normal buffer.
+        *
+        * Once the port is marked inactive we don't need to keep it locked.
         */
        if (IP_PREALLOC(port)) {
                ipc_port_t inuse_port;
@@ -929,24 +1039,48 @@ ipc_port_destroy(
                kmsg = port->ip_premsg;
                assert(kmsg != IKM_NULL);
                inuse_port = ikm_prealloc_inuse_port(kmsg);
-               IP_CLEAR_PREALLOC(port, kmsg);
-               ip_unlock(port);
+               ipc_kmsg_clear_prealloc(kmsg, port);
+
+               imq_lock(&port->ip_messages);
+               ipc_port_send_turnstile_recompute_push_locked(port);
+               /* mqueue and port unlocked */
+
                if (inuse_port != IP_NULL) {
                        assert(inuse_port == port);
                } else {
                        ipc_kmsg_free(kmsg);
                }
        } else {
-               ip_unlock(port);
+               imq_lock(&port->ip_messages);
+               ipc_port_send_turnstile_recompute_push_locked(port);
+               /* mqueue and port unlocked */
+       }
+
+       /* Deallocate the watchport element */
+       if (watchport_elem) {
+               task_watchport_elem_deallocate(watchport_elem);
+               watchport_elem = NULL;
+       }
+
+       /* unlink the kmsg from special reply port */
+       if (special_reply) {
+               ipc_port_adjust_special_reply_port(port,
+                   IPC_PORT_ADJUST_SR_ALLOW_SYNC_LINKAGE);
        }
 
        /* throw away no-senders request */
-       if (nsrequest != IP_NULL)
+       if (nsrequest != IP_NULL) {
                ipc_notify_send_once(nsrequest); /* consumes ref */
+       }
+       /*
+        * Reap any kmsg objects waiting to be destroyed.
+        * This must be done after we've released the port lock.
+        */
+       if (reap_msgs) {
+               ipc_kmsg_reap_delayed();
+       }
 
-       /* destroy any queued messages */
        mqueue = &port->ip_messages;
-       ipc_mqueue_destroy(mqueue);
 
        /* cleanup waitq related resources */
        ipc_mqueue_deinit(mqueue);
@@ -958,7 +1092,7 @@ ipc_port_destroy(
 
        ip_release(port); /* consume caller's ref */
 
- drop_assertions:
+drop_assertions:
 #if IMPORTANCE_INHERITANCE
        if (release_imp_task != IIT_NULL) {
                if (assertcnt > 0) {
@@ -968,7 +1102,6 @@ ipc_port_destroy(
                        ipc_importance_task_drop_internal_assertion(release_imp_task, assertcnt);
                }
                ipc_importance_task_release(release_imp_task);
-
        } else if (assertcnt > 0) {
                if (top) {
                        self->ith_assertions = 0;
@@ -994,46 +1127,44 @@ ipc_port_destroy(
  *             but guaranteeing that this doesn't create a circle
  *             port->ip_destination->ip_destination->... == port
  *
- *             Additionally, if port was successfully changed to "in transit",
- *             propagate boost assertions from the "in limbo" port to all
- *             the ports in the chain, and, if the destination task accepts
- *             boosts, to the destination task.
- *
  *     Conditions:
  *             No ports locked.  References held for "port" and "dest".
  */
 
 boolean_t
 ipc_port_check_circularity(
-       ipc_port_t      port,
-       ipc_port_t      dest)
+       ipc_port_t      port,
+       ipc_port_t      dest)
 {
-       ipc_port_t base;
-
 #if IMPORTANCE_INHERITANCE
-       ipc_importance_task_t imp_task = IIT_NULL;
-       ipc_importance_task_t release_imp_task = IIT_NULL;
-       int assertcnt = 0;
-#endif /* IMPORTANCE_INHERITANCE */
+       /* adjust importance counts at the same time */
+       return ipc_importance_check_circularity(port, dest);
+#else
+       ipc_port_t base;
+       struct task_watchport_elem *watchport_elem = NULL;
 
        assert(port != IP_NULL);
        assert(dest != IP_NULL);
 
-       if (port == dest)
+       if (port == dest) {
                return TRUE;
+       }
        base = dest;
 
+       /* Check if destination needs a turnstile */
+       ipc_port_send_turnstile_prepare(dest);
+
        /*
         *      First try a quick check that can run in parallel.
         *      No circularity if dest is not in transit.
         */
-
        ip_lock(port);
        if (ip_lock_try(dest)) {
                if (!ip_active(dest) ||
                    (dest->ip_receiver_name != MACH_PORT_NULL) ||
-                   (dest->ip_destination == IP_NULL))
+                   (dest->ip_destination == IP_NULL)) {
                        goto not_circular;
+               }
 
                /* dest is in transit; further checking necessary */
 
@@ -1053,8 +1184,9 @@ ipc_port_check_circularity(
 
                if (!ip_active(base) ||
                    (base->ip_receiver_name != MACH_PORT_NULL) ||
-                   (base->ip_destination == IP_NULL))
+                   (base->ip_destination == IP_NULL)) {
                        break;
+               }
 
                base = base->ip_destination;
        }
@@ -1067,24 +1199,24 @@ ipc_port_check_circularity(
                ipc_port_multiple_unlock();
 
                /* port (== base) is in limbo */
-
-               assert(ip_active(port));
+               require_ip_active(port);
                assert(port->ip_receiver_name == MACH_PORT_NULL);
                assert(port->ip_destination == IP_NULL);
 
-               while (dest != IP_NULL) {
+               base = dest;
+               while (base != IP_NULL) {
                        ipc_port_t next;
 
                        /* dest is in transit or in limbo */
+                       require_ip_active(base);
+                       assert(base->ip_receiver_name == MACH_PORT_NULL);
 
-                       assert(ip_active(dest));
-                       assert(dest->ip_receiver_name == MACH_PORT_NULL);
-
-                       next = dest->ip_destination;
-                       ip_unlock(dest);
-                       dest = next;
+                       next = base->ip_destination;
+                       ip_unlock(base);
+                       base = next;
                }
 
+               ipc_port_send_turnstile_complete(dest);
                return TRUE;
        }
 
@@ -1097,215 +1229,995 @@ ipc_port_check_circularity(
        ip_lock(port);
        ipc_port_multiple_unlock();
 
-    not_circular:
+not_circular:
+       imq_lock(&port->ip_messages);
 
        /* port is in limbo */
-
-       assert(ip_active(port));
+       require_ip_active(port);
        assert(port->ip_receiver_name == MACH_PORT_NULL);
        assert(port->ip_destination == IP_NULL);
 
+       /* Clear the watchport boost */
+       watchport_elem = ipc_port_clear_watchport_elem_internal(port);
+
+       /* Check if the port is being enqueued as a part of sync bootstrap checkin */
+       if (dest->ip_specialreply && dest->ip_sync_bootstrap_checkin) {
+               port->ip_sync_bootstrap_checkin = 1;
+       }
+
        ip_reference(dest);
        port->ip_destination = dest;
 
-#if IMPORTANCE_INHERITANCE
-       /* must have been in limbo or still bound to a task */
-       assert(port->ip_tempowner != 0);
+       /* Setup linkage for source port if it has sync ipc push */
+       struct turnstile *send_turnstile = TURNSTILE_NULL;
+       if (port_send_turnstile(port)) {
+               send_turnstile = turnstile_prepare((uintptr_t)port,
+                   port_send_turnstile_address(port),
+                   TURNSTILE_NULL, TURNSTILE_SYNC_IPC);
 
-       /*
-        * We delayed dropping assertions from a specific task.
-        * Cache that info now (we'll drop assertions and the
-        * task reference below).
-        */
-       release_imp_task = port->ip_imp_task;
-       if (IIT_NULL != release_imp_task) {
-               port->ip_imp_task = IIT_NULL;
-       }
-       assertcnt = port->ip_impcount;
+               /*
+                * What ipc_port_adjust_port_locked would do,
+                * but we need to also drop even more locks before
+                * calling turnstile_update_inheritor_complete().
+                */
+               ipc_port_adjust_sync_link_state_locked(port, PORT_SYNC_LINK_ANY, NULL);
 
-       /* take the port out of limbo w.r.t. assertions */
-       port->ip_tempowner = 0;
+               turnstile_update_inheritor(send_turnstile, port_send_turnstile(dest),
+                   (TURNSTILE_INHERITOR_TURNSTILE | TURNSTILE_IMMEDIATE_UPDATE));
 
-#endif /* IMPORTANCE_INHERITANCE */
+               /* update complete and turnstile complete called after dropping all locks */
+       }
+       imq_unlock(&port->ip_messages);
 
        /* now unlock chain */
 
        ip_unlock(port);
 
        for (;;) {
+               ipc_port_t next;
 
-#if IMPORTANCE_INHERITANCE
-               /* every port along chain track assertions behind it */
-               dest->ip_impcount += assertcnt;
-#endif /* IMPORTANCE_INHERITANCE */
-
-               if (dest == base)
+               if (dest == base) {
                        break;
+               }
 
                /* port is in transit */
-
-               assert(ip_active(dest));
+               require_ip_active(dest);
                assert(dest->ip_receiver_name == MACH_PORT_NULL);
                assert(dest->ip_destination != IP_NULL);
 
-#if IMPORTANCE_INHERITANCE
-               assert(dest->ip_tempowner == 0);
-#endif /* IMPORTANCE_INHERITANCE */
-
-               port = dest->ip_destination;
+               next = dest->ip_destination;
                ip_unlock(dest);
-               dest = port;
+               dest = next;
        }
 
        /* base is not in transit */
        assert(!ip_active(base) ||
-              (base->ip_receiver_name != MACH_PORT_NULL) ||
-              (base->ip_destination == IP_NULL));
-
-#if IMPORTANCE_INHERITANCE
-       /*
-        * Find the task to boost (if any).
-        * We will boost "through" ports that don't know
-        * about inheritance to deliver receive rights that
-        * do.
-        */
-       if (ip_active(base) && (assertcnt > 0)) {
-               if (base->ip_tempowner != 0) {
-                       if (IIT_NULL != base->ip_imp_task) {
-                               /* specified tempowner task */
-                               imp_task = base->ip_imp_task;
-                               assert(ipc_importance_task_is_any_receiver_type(imp_task));
-                       }
-                       /* otherwise don't boost current task */
-
-               } else if (base->ip_receiver_name != MACH_PORT_NULL) {
-                       ipc_space_t space = base->ip_receiver;
-
-                       /* only spaces with boost-accepting tasks */
-                       if (space->is_task != TASK_NULL &&
-                           ipc_importance_task_is_any_receiver_type(space->is_task->task_imp_base))
-                               imp_task = space->is_task->task_imp_base;
-               }
-
-               /* take reference before unlocking base */
-               if (imp_task != IIT_NULL) {
-                       ipc_importance_task_reference(imp_task);
-               }
-       }
-#endif /* IMPORTANCE_INHERITANCE */
+           (base->ip_receiver_name != MACH_PORT_NULL) ||
+           (base->ip_destination == IP_NULL));
 
        ip_unlock(base);
 
-#if IMPORTANCE_INHERITANCE
-       /*
-        * Transfer assertions now that the ports are unlocked.
-        * Avoid extra overhead if transferring to/from the same task.
-        */
-       boolean_t transfer_assertions = (imp_task != release_imp_task) ? TRUE : FALSE;
+       /* All locks dropped, call turnstile_update_inheritor_complete for source port's turnstile */
+       if (send_turnstile) {
+               turnstile_update_inheritor_complete(send_turnstile, TURNSTILE_INTERLOCK_NOT_HELD);
 
-       if (imp_task != IIT_NULL) {
-               if (transfer_assertions)
-                       ipc_importance_task_hold_internal_assertion(imp_task, assertcnt);
-               ipc_importance_task_release(imp_task);
-               imp_task = IIT_NULL;
+               /* Take the mq lock to call turnstile complete */
+               imq_lock(&port->ip_messages);
+               turnstile_complete((uintptr_t)port, port_send_turnstile_address(port), NULL, TURNSTILE_SYNC_IPC);
+               send_turnstile = TURNSTILE_NULL;
+               imq_unlock(&port->ip_messages);
+               turnstile_cleanup();
        }
 
-       if (release_imp_task != IIT_NULL) {
-               if (transfer_assertions)
-                       ipc_importance_task_drop_internal_assertion(release_imp_task, assertcnt);
-               ipc_importance_task_release(release_imp_task);
-               release_imp_task = IIT_NULL;
+       if (watchport_elem) {
+               task_watchport_elem_deallocate(watchport_elem);
        }
-#endif /* IMPORTANCE_INHERITANCE */
 
        return FALSE;
+#endif /* !IMPORTANCE_INHERITANCE */
 }
 
 /*
- *     Routine:        ipc_port_impcount_delta
+ *     Routine:        ipc_port_watchport_elem
  *     Purpose:
- *             Adjust only the importance count associated with a port.
- *             If there are any adjustments to be made to receiver task,
- *             those are handled elsewhere.
+ *             Get the port's watchport elem field
  *
- *             For now, be defensive during deductions to make sure the
- *             impcount for the port doesn't underflow zero.  This will
- *             go away when the port boost addition is made atomic (see
- *             note in ipc_port_importance_delta()).
  *     Conditions:
- *             The port is referenced and locked.
- *             Nothing else is locked.
+ *             mqueue locked
  */
-mach_port_delta_t
-ipc_port_impcount_delta(
-       ipc_port_t        port,
-       mach_port_delta_t delta,
-       ipc_port_t        __unused base)
+static struct task_watchport_elem *
+ipc_port_watchport_elem(ipc_port_t port)
 {
-       mach_port_delta_t absdelta; 
-
-       if (!ip_active(port)) {
-               return 0;
-       }
+       return port->ip_messages.imq_wait_queue.waitq_tspriv;
+}
 
-       /* adding/doing nothing is easy */
-       if (delta >= 0) {
-               port->ip_impcount += delta;
-               return delta;
-       }
+/*
+ *     Routine:        ipc_port_update_watchport_elem
+ *     Purpose:
+ *             Set the port's watchport elem field
+ *
+ *     Conditions:
+ *             mqueue locked
+ */
+static inline struct task_watchport_elem *
+ipc_port_update_watchport_elem(ipc_port_t port, struct task_watchport_elem *we)
+{
+       struct task_watchport_elem *old_we = ipc_port_watchport_elem(port);
+       port->ip_messages.imq_wait_queue.waitq_tspriv = we;
+       return old_we;
+}
 
-       absdelta = 0 - delta;           
-       //assert(port->ip_impcount >= absdelta);
-       /* if we have enough to deduct, we're done */
-       if (port->ip_impcount >= absdelta) {
-               port->ip_impcount -= absdelta;
-               return delta;
-       }
+/*
+ * Update the recv turnstile inheritor for a port.
+ *
+ * Sync IPC through the port receive turnstile only happens for the special
+ * reply port case. It has three sub-cases:
+ *
+ * 1. a send-once right is in transit, and pushes on the send turnstile of its
+ *    destination mqueue.
+ *
+ * 2. a send-once right has been stashed on a knote it was copied out "through",
+ *    as the first such copied out port.
+ *
+ * 3. a send-once right has been stashed on a knote it was copied out "through",
+ *    as the second or more copied out port.
+ */
+void
+ipc_port_recv_update_inheritor(
+       ipc_port_t port,
+       struct turnstile *rcv_turnstile,
+       turnstile_update_flags_t flags)
+{
+       struct turnstile *inheritor = TURNSTILE_NULL;
+       struct knote *kn;
 
-#if DEVELOPMENT || DEBUG
-       if (port->ip_receiver_name != MACH_PORT_NULL) {
-               task_t target_task = port->ip_receiver->is_task;
-               ipc_importance_task_t target_imp = target_task->task_imp_base;
-               const char *target_procname;
-               int target_pid;
+       if (ip_active(port) && port->ip_specialreply) {
+               imq_held(&port->ip_messages);
 
-               if (target_imp != IIT_NULL) {
-                       target_procname = target_imp->iit_procname;
-                       target_pid = target_imp->iit_bsd_pid;
-               } else {
-                       target_procname = "unknown";
-                       target_pid = -1;
-               }
-               printf("Over-release of importance assertions for port 0x%x receiver pid %d (%s), "
-                      "dropping %d assertion(s) but port only has %d remaining.\n",
-                      port->ip_receiver_name, 
-                      target_imp->iit_bsd_pid, target_imp->iit_procname,
-                      absdelta, port->ip_impcount);
+               switch (port->ip_sync_link_state) {
+               case PORT_SYNC_LINK_PORT:
+                       if (port->ip_sync_inheritor_port != NULL) {
+                               inheritor = port_send_turnstile(port->ip_sync_inheritor_port);
+                       }
+                       break;
 
-       } else if (base != IP_NULL) {
-               task_t target_task = base->ip_receiver->is_task;
-               ipc_importance_task_t target_imp = target_task->task_imp_base;
-               const char *target_procname;
-               int target_pid;
+               case PORT_SYNC_LINK_WORKLOOP_KNOTE:
+                       kn = port->ip_sync_inheritor_knote;
+                       inheritor = filt_ipc_kqueue_turnstile(kn);
+                       break;
 
-               if (target_imp != IIT_NULL) {
-                       target_procname = target_imp->iit_procname;
-                       target_pid = target_imp->iit_bsd_pid;
-               } else {
-                       target_procname = "unknown";
-                       target_pid = -1;
+               case PORT_SYNC_LINK_WORKLOOP_STASH:
+                       inheritor = port->ip_sync_inheritor_ts;
+                       break;
                }
-               printf("Over-release of importance assertions for port %p "
-                      "enqueued on port 0x%x with receiver pid %d (%s), "
-                      "dropping %d assertion(s) but port only has %d remaining.\n",
-                      port, base->ip_receiver_name, 
-                      target_imp->iit_bsd_pid, target_imp->iit_procname,
-                      absdelta, port->ip_impcount);
        }
-#endif
-       delta = 0 - port->ip_impcount;
-       port->ip_impcount = 0;
-       return delta;
+
+       turnstile_update_inheritor(rcv_turnstile, inheritor,
+           flags | TURNSTILE_INHERITOR_TURNSTILE);
+}
+
+/*
+ * Update the send turnstile inheritor for a port.
+ *
+ * Sync IPC through the port send turnstile has 7 possible reasons to be linked:
+ *
+ * 1. a special reply port is part of sync ipc for bootstrap checkin and needs
+ *    to push on thread doing the sync ipc.
+ *
+ * 2. a receive right is in transit, and pushes on the send turnstile of its
+ *    destination mqueue.
+ *
+ * 3. port was passed as an exec watchport and port is pushing on main thread
+ *    of the task.
+ *
+ * 4. a receive right has been stashed on a knote it was copied out "through",
+ *    as the first such copied out port (same as PORT_SYNC_LINK_WORKLOOP_KNOTE
+ *    for the special reply port)
+ *
+ * 5. a receive right has been stashed on a knote it was copied out "through",
+ *    as the second or more copied out port (same as
+ *    PORT_SYNC_LINK_WORKLOOP_STASH for the special reply port)
+ *
+ * 6. a receive right has been copied out as a part of sync bootstrap checkin
+ *    and needs to push on thread doing the sync bootstrap checkin.
+ *
+ * 7. the receive right is monitored by a knote, and pushes on any that is
+ *    registered on a workloop. filt_machport makes sure that if such a knote
+ *    exists, it is kept as the first item in the knote list, so we never need
+ *    to walk.
+ */
+void
+ipc_port_send_update_inheritor(
+       ipc_port_t port,
+       struct turnstile *send_turnstile,
+       turnstile_update_flags_t flags)
+{
+       ipc_mqueue_t mqueue = &port->ip_messages;
+       turnstile_inheritor_t inheritor = TURNSTILE_INHERITOR_NULL;
+       struct knote *kn;
+       turnstile_update_flags_t inheritor_flags = TURNSTILE_INHERITOR_TURNSTILE;
+
+       assert(imq_held(mqueue));
+
+       if (!ip_active(port)) {
+               /* this port is no longer active, it should not push anywhere */
+       } else if (port->ip_specialreply) {
+               /* Case 1. */
+               if (port->ip_sync_bootstrap_checkin && prioritize_launch) {
+                       inheritor = port->ip_messages.imq_srp_owner_thread;
+                       inheritor_flags = TURNSTILE_INHERITOR_THREAD;
+               }
+       } else if (port->ip_receiver_name == MACH_PORT_NULL &&
+           port->ip_destination != NULL) {
+               /* Case 2. */
+               inheritor = port_send_turnstile(port->ip_destination);
+       } else if (ipc_port_watchport_elem(port) != NULL) {
+               /* Case 3. */
+               if (prioritize_launch) {
+                       assert(port->ip_sync_link_state == PORT_SYNC_LINK_ANY);
+                       inheritor = ipc_port_get_watchport_inheritor(port);
+                       inheritor_flags = TURNSTILE_INHERITOR_THREAD;
+               }
+       } else if (port->ip_sync_link_state == PORT_SYNC_LINK_WORKLOOP_KNOTE) {
+               /* Case 4. */
+               inheritor = filt_ipc_kqueue_turnstile(mqueue->imq_inheritor_knote);
+       } else if (port->ip_sync_link_state == PORT_SYNC_LINK_WORKLOOP_STASH) {
+               /* Case 5. */
+               inheritor = mqueue->imq_inheritor_turnstile;
+       } else if (port->ip_sync_link_state == PORT_SYNC_LINK_RCV_THREAD) {
+               /* Case 6. */
+               if (prioritize_launch) {
+                       inheritor = port->ip_messages.imq_inheritor_thread_ref;
+                       inheritor_flags = TURNSTILE_INHERITOR_THREAD;
+               }
+       } else if ((kn = SLIST_FIRST(&mqueue->imq_klist))) {
+               /* Case 7. Push on a workloop that is interested */
+               if (filt_machport_kqueue_has_turnstile(kn)) {
+                       assert(port->ip_sync_link_state == PORT_SYNC_LINK_ANY);
+                       inheritor = filt_ipc_kqueue_turnstile(kn);
+               }
+       }
+
+       turnstile_update_inheritor(send_turnstile, inheritor,
+           flags | inheritor_flags);
+}
+
+/*
+ *     Routine:        ipc_port_send_turnstile_prepare
+ *     Purpose:
+ *             Get a reference on port's send turnstile, if
+ *             port does not have a send turnstile then allocate one.
+ *
+ *     Conditions:
+ *             Nothing is locked.
+ */
+void
+ipc_port_send_turnstile_prepare(ipc_port_t port)
+{
+       struct turnstile *turnstile = TURNSTILE_NULL;
+       struct turnstile *send_turnstile = TURNSTILE_NULL;
+
+retry_alloc:
+       imq_lock(&port->ip_messages);
+
+       if (port_send_turnstile(port) == NULL ||
+           port_send_turnstile(port)->ts_port_ref == 0) {
+               if (turnstile == TURNSTILE_NULL) {
+                       imq_unlock(&port->ip_messages);
+                       turnstile = turnstile_alloc();
+                       goto retry_alloc;
+               }
+
+               send_turnstile = turnstile_prepare((uintptr_t)port,
+                   port_send_turnstile_address(port),
+                   turnstile, TURNSTILE_SYNC_IPC);
+               turnstile = TURNSTILE_NULL;
+
+               ipc_port_send_update_inheritor(port, send_turnstile,
+                   TURNSTILE_IMMEDIATE_UPDATE);
+
+               /* turnstile complete will be called in ipc_port_send_turnstile_complete */
+       }
+
+       /* Increment turnstile counter */
+       port_send_turnstile(port)->ts_port_ref++;
+       imq_unlock(&port->ip_messages);
+
+       if (send_turnstile) {
+               turnstile_update_inheritor_complete(send_turnstile,
+                   TURNSTILE_INTERLOCK_NOT_HELD);
+       }
+       if (turnstile != TURNSTILE_NULL) {
+               turnstile_deallocate(turnstile);
+       }
+}
+
+
+/*
+ *     Routine:        ipc_port_send_turnstile_complete
+ *     Purpose:
+ *             Drop a ref on the port's send turnstile, if the
+ *             ref becomes zero, deallocate the turnstile.
+ *
+ *     Conditions:
+ *             The space might be locked, use safe deallocate.
+ */
+void
+ipc_port_send_turnstile_complete(ipc_port_t port)
+{
+       struct turnstile *turnstile = TURNSTILE_NULL;
+
+       /* Drop turnstile count on dest port */
+       imq_lock(&port->ip_messages);
+
+       port_send_turnstile(port)->ts_port_ref--;
+       if (port_send_turnstile(port)->ts_port_ref == 0) {
+               turnstile_complete((uintptr_t)port, port_send_turnstile_address(port),
+                   &turnstile, TURNSTILE_SYNC_IPC);
+               assert(turnstile != TURNSTILE_NULL);
+       }
+       imq_unlock(&port->ip_messages);
+       turnstile_cleanup();
+
+       if (turnstile != TURNSTILE_NULL) {
+               turnstile_deallocate_safe(turnstile);
+               turnstile = TURNSTILE_NULL;
+       }
+}
+
+/*
+ *     Routine:        ipc_port_rcv_turnstile
+ *     Purpose:
+ *             Get the port's receive turnstile
+ *
+ *     Conditions:
+ *             mqueue locked or thread waiting on turnstile is locked.
+ */
+static struct turnstile *
+ipc_port_rcv_turnstile(ipc_port_t port)
+{
+       return *port_rcv_turnstile_address(port);
+}
+
+
+/*
+ *     Routine:        ipc_port_link_special_reply_port
+ *     Purpose:
+ *             Link the special reply port with the destination port.
+ *              Allocates turnstile to dest port.
+ *
+ *     Conditions:
+ *             Nothing is locked.
+ */
+void
+ipc_port_link_special_reply_port(
+       ipc_port_t special_reply_port,
+       ipc_port_t dest_port,
+       boolean_t sync_bootstrap_checkin)
+{
+       boolean_t drop_turnstile_ref = FALSE;
+
+       /* Check if dest_port needs a turnstile */
+       ipc_port_send_turnstile_prepare(dest_port);
+
+       /* Lock the special reply port and establish the linkage */
+       ip_lock(special_reply_port);
+       imq_lock(&special_reply_port->ip_messages);
+
+       if (sync_bootstrap_checkin && special_reply_port->ip_specialreply) {
+               special_reply_port->ip_sync_bootstrap_checkin = 1;
+       }
+
+       /* Check if we need to drop the acquired turnstile ref on dest port */
+       if (!special_reply_port->ip_specialreply ||
+           special_reply_port->ip_sync_link_state != PORT_SYNC_LINK_ANY ||
+           special_reply_port->ip_sync_inheritor_port != IPC_PORT_NULL) {
+               drop_turnstile_ref = TRUE;
+       } else {
+               /* take a reference on dest_port */
+               ip_reference(dest_port);
+               special_reply_port->ip_sync_inheritor_port = dest_port;
+               special_reply_port->ip_sync_link_state = PORT_SYNC_LINK_PORT;
+       }
+
+       imq_unlock(&special_reply_port->ip_messages);
+       ip_unlock(special_reply_port);
+
+       if (drop_turnstile_ref) {
+               ipc_port_send_turnstile_complete(dest_port);
+       }
+
+       return;
+}
+
+#if DEVELOPMENT || DEBUG
+inline void
+ipc_special_reply_port_bits_reset(ipc_port_t special_reply_port)
+{
+       special_reply_port->ip_srp_lost_link = 0;
+       special_reply_port->ip_srp_msg_sent = 0;
+}
+
+static inline void
+ipc_special_reply_port_msg_sent_reset(ipc_port_t special_reply_port)
+{
+       if (special_reply_port->ip_specialreply == 1) {
+               special_reply_port->ip_srp_msg_sent = 0;
+       }
+}
+
+inline void
+ipc_special_reply_port_msg_sent(ipc_port_t special_reply_port)
+{
+       if (special_reply_port->ip_specialreply == 1) {
+               special_reply_port->ip_srp_msg_sent = 1;
+       }
+}
+
+static inline void
+ipc_special_reply_port_lost_link(ipc_port_t special_reply_port)
+{
+       if (special_reply_port->ip_specialreply == 1 && special_reply_port->ip_srp_msg_sent == 0) {
+               special_reply_port->ip_srp_lost_link = 1;
+       }
+}
+
+#else /* DEVELOPMENT || DEBUG */
+inline void
+ipc_special_reply_port_bits_reset(__unused ipc_port_t special_reply_port)
+{
+       return;
+}
+
+static inline void
+ipc_special_reply_port_msg_sent_reset(__unused ipc_port_t special_reply_port)
+{
+       return;
+}
+
+inline void
+ipc_special_reply_port_msg_sent(__unused ipc_port_t special_reply_port)
+{
+       return;
+}
+
+static inline void
+ipc_special_reply_port_lost_link(__unused ipc_port_t special_reply_port)
+{
+       return;
+}
+#endif /* DEVELOPMENT || DEBUG */
+
+/*
+ *     Routine:        ipc_port_adjust_special_reply_port_locked
+ *     Purpose:
+ *             If the special port has a turnstile, update its inheritor.
+ *     Condition:
+ *             Special reply port locked on entry.
+ *             Special reply port unlocked on return.
+ *             The passed in port is a special reply port.
+ *     Returns:
+ *             None.
+ */
+void
+ipc_port_adjust_special_reply_port_locked(
+       ipc_port_t special_reply_port,
+       struct knote *kn,
+       uint8_t flags,
+       boolean_t get_turnstile)
+{
+       ipc_port_t dest_port = IPC_PORT_NULL;
+       int sync_link_state = PORT_SYNC_LINK_NO_LINKAGE;
+       turnstile_inheritor_t inheritor = TURNSTILE_INHERITOR_NULL;
+       struct turnstile *ts = TURNSTILE_NULL;
+
+       ip_lock_held(special_reply_port); // ip_sync_link_state is touched
+       imq_lock(&special_reply_port->ip_messages);
+
+       if (!special_reply_port->ip_specialreply) {
+               // only mach_msg_receive_results_complete() calls this with any port
+               assert(get_turnstile);
+               goto not_special;
+       }
+
+       if (flags & IPC_PORT_ADJUST_SR_RECEIVED_MSG) {
+               ipc_special_reply_port_msg_sent_reset(special_reply_port);
+       }
+
+       if (flags & IPC_PORT_ADJUST_UNLINK_THREAD) {
+               special_reply_port->ip_messages.imq_srp_owner_thread = NULL;
+       }
+
+       if (flags & IPC_PORT_ADJUST_RESET_BOOSTRAP_CHECKIN) {
+               special_reply_port->ip_sync_bootstrap_checkin = 0;
+       }
+
+       /* Check if the special reply port is marked non-special */
+       if (special_reply_port->ip_sync_link_state == PORT_SYNC_LINK_ANY) {
+not_special:
+               if (get_turnstile) {
+                       turnstile_complete((uintptr_t)special_reply_port,
+                           port_rcv_turnstile_address(special_reply_port), NULL, TURNSTILE_SYNC_IPC);
+               }
+               imq_unlock(&special_reply_port->ip_messages);
+               ip_unlock(special_reply_port);
+               if (get_turnstile) {
+                       turnstile_cleanup();
+               }
+               return;
+       }
+
+       if (flags & IPC_PORT_ADJUST_SR_LINK_WORKLOOP) {
+               if (ITH_KNOTE_VALID(kn, MACH_MSG_TYPE_PORT_SEND_ONCE)) {
+                       inheritor = filt_machport_stash_port(kn, special_reply_port,
+                           &sync_link_state);
+               }
+       } else if (flags & IPC_PORT_ADJUST_SR_ALLOW_SYNC_LINKAGE) {
+               sync_link_state = PORT_SYNC_LINK_ANY;
+       }
+
+       /* Check if need to break linkage */
+       if (!get_turnstile && sync_link_state == PORT_SYNC_LINK_NO_LINKAGE &&
+           special_reply_port->ip_sync_link_state == PORT_SYNC_LINK_NO_LINKAGE) {
+               imq_unlock(&special_reply_port->ip_messages);
+               ip_unlock(special_reply_port);
+               return;
+       }
+
+       switch (special_reply_port->ip_sync_link_state) {
+       case PORT_SYNC_LINK_PORT:
+               dest_port = special_reply_port->ip_sync_inheritor_port;
+               special_reply_port->ip_sync_inheritor_port = IPC_PORT_NULL;
+               break;
+       case PORT_SYNC_LINK_WORKLOOP_KNOTE:
+               special_reply_port->ip_sync_inheritor_knote = NULL;
+               break;
+       case PORT_SYNC_LINK_WORKLOOP_STASH:
+               special_reply_port->ip_sync_inheritor_ts = NULL;
+               break;
+       }
+
+       special_reply_port->ip_sync_link_state = sync_link_state;
+
+       switch (sync_link_state) {
+       case PORT_SYNC_LINK_WORKLOOP_KNOTE:
+               special_reply_port->ip_sync_inheritor_knote = kn;
+               break;
+       case PORT_SYNC_LINK_WORKLOOP_STASH:
+               special_reply_port->ip_sync_inheritor_ts = inheritor;
+               break;
+       case PORT_SYNC_LINK_NO_LINKAGE:
+               if (flags & IPC_PORT_ADJUST_SR_ENABLE_EVENT) {
+                       ipc_special_reply_port_lost_link(special_reply_port);
+               }
+               break;
+       }
+
+       /* Get thread's turnstile donated to special reply port */
+       if (get_turnstile) {
+               turnstile_complete((uintptr_t)special_reply_port,
+                   port_rcv_turnstile_address(special_reply_port), NULL, TURNSTILE_SYNC_IPC);
+       } else {
+               ts = ipc_port_rcv_turnstile(special_reply_port);
+               if (ts) {
+                       turnstile_reference(ts);
+                       ipc_port_recv_update_inheritor(special_reply_port, ts,
+                           TURNSTILE_IMMEDIATE_UPDATE);
+               }
+       }
+
+       imq_unlock(&special_reply_port->ip_messages);
+       ip_unlock(special_reply_port);
+
+       if (get_turnstile) {
+               turnstile_cleanup();
+       } else if (ts) {
+               /* Call turnstile cleanup after dropping the interlock */
+               turnstile_update_inheritor_complete(ts, TURNSTILE_INTERLOCK_NOT_HELD);
+               turnstile_deallocate_safe(ts);
+       }
+
+       /* Release the ref on the dest port and its turnstile */
+       if (dest_port) {
+               ipc_port_send_turnstile_complete(dest_port);
+               /* release the reference on the dest port */
+               ip_release(dest_port);
+       }
+}
+
+/*
+ *     Routine:        ipc_port_adjust_special_reply_port
+ *     Purpose:
+ *             If the special port has a turnstile, update its inheritor.
+ *     Condition:
+ *             Nothing locked.
+ *     Returns:
+ *             None.
+ */
+void
+ipc_port_adjust_special_reply_port(
+       ipc_port_t port,
+       uint8_t flags)
+{
+       if (port->ip_specialreply) {
+               ip_lock(port);
+               ipc_port_adjust_special_reply_port_locked(port, NULL, flags, FALSE);
+       }
+}
+
+/*
+ *     Routine:        ipc_port_adjust_sync_link_state_locked
+ *     Purpose:
+ *             Update the sync link state of the port and the
+ *             turnstile inheritor.
+ *     Condition:
+ *             Port and mqueue locked on entry.
+ *             Port and mqueue locked on return.
+ *     Returns:
+ *              None.
+ */
+void
+ipc_port_adjust_sync_link_state_locked(
+       ipc_port_t port,
+       int sync_link_state,
+       turnstile_inheritor_t inheritor)
+{
+       switch (port->ip_sync_link_state) {
+       case PORT_SYNC_LINK_RCV_THREAD:
+               /* deallocate the thread reference for the inheritor */
+               thread_deallocate_safe(port->ip_messages.imq_inheritor_thread_ref);
+       /* Fall through */
+
+       default:
+               klist_init(&port->ip_messages.imq_klist);
+       }
+
+       switch (sync_link_state) {
+       case PORT_SYNC_LINK_WORKLOOP_KNOTE:
+               port->ip_messages.imq_inheritor_knote = inheritor;
+               break;
+       case PORT_SYNC_LINK_WORKLOOP_STASH:
+               port->ip_messages.imq_inheritor_turnstile = inheritor;
+               break;
+       case PORT_SYNC_LINK_RCV_THREAD:
+               /* The thread could exit without clearing port state, take a thread ref */
+               thread_reference((thread_t)inheritor);
+               port->ip_messages.imq_inheritor_thread_ref = inheritor;
+               break;
+       default:
+               klist_init(&port->ip_messages.imq_klist);
+               sync_link_state = PORT_SYNC_LINK_ANY;
+       }
+
+       port->ip_sync_link_state = sync_link_state;
+}
+
+
+/*
+ *     Routine:        ipc_port_adjust_port_locked
+ *     Purpose:
+ *             If the port has a turnstile, update its inheritor.
+ *     Condition:
+ *             Port locked on entry.
+ *             Port unlocked on return.
+ *     Returns:
+ *             None.
+ */
+void
+ipc_port_adjust_port_locked(
+       ipc_port_t port,
+       struct knote *kn,
+       boolean_t sync_bootstrap_checkin)
+{
+       int sync_link_state = PORT_SYNC_LINK_ANY;
+       turnstile_inheritor_t inheritor = TURNSTILE_INHERITOR_NULL;
+
+       ip_lock_held(port); // ip_sync_link_state is touched
+       imq_held(&port->ip_messages);
+
+       assert(!port->ip_specialreply);
+
+       if (kn) {
+               inheritor = filt_machport_stash_port(kn, port, &sync_link_state);
+               if (sync_link_state == PORT_SYNC_LINK_WORKLOOP_KNOTE) {
+                       inheritor = kn;
+               }
+       } else if (sync_bootstrap_checkin) {
+               inheritor = current_thread();
+               sync_link_state = PORT_SYNC_LINK_RCV_THREAD;
+       }
+
+       ipc_port_adjust_sync_link_state_locked(port, sync_link_state, inheritor);
+       port->ip_sync_bootstrap_checkin = 0;
+
+       ipc_port_send_turnstile_recompute_push_locked(port);
+       /* port and mqueue unlocked */
+}
+
+/*
+ *     Routine:        ipc_port_clear_sync_rcv_thread_boost_locked
+ *     Purpose:
+ *             If the port is pushing on rcv thread, clear it.
+ *     Condition:
+ *             Port locked on entry
+ *             mqueue is not locked.
+ *             Port unlocked on return.
+ *     Returns:
+ *             None.
+ */
+void
+ipc_port_clear_sync_rcv_thread_boost_locked(
+       ipc_port_t port)
+{
+       ip_lock_held(port); // ip_sync_link_state is touched
+
+       if (port->ip_sync_link_state != PORT_SYNC_LINK_RCV_THREAD) {
+               ip_unlock(port);
+               return;
+       }
+
+       imq_lock(&port->ip_messages);
+       ipc_port_adjust_sync_link_state_locked(port, PORT_SYNC_LINK_ANY, NULL);
+
+       ipc_port_send_turnstile_recompute_push_locked(port);
+       /* port and mqueue unlocked */
+}
+
+/*
+ *     Routine:        ipc_port_add_watchport_elem_locked
+ *     Purpose:
+ *             Transfer the turnstile boost of watchport to task calling exec.
+ *     Condition:
+ *             Port locked on entry.
+ *             Port unlocked on return.
+ *     Returns:
+ *             KERN_SUCESS on success.
+ *             KERN_FAILURE otherwise.
+ */
+kern_return_t
+ipc_port_add_watchport_elem_locked(
+       ipc_port_t                 port,
+       struct task_watchport_elem *watchport_elem,
+       struct task_watchport_elem **old_elem)
+{
+       ip_lock_held(port);
+       imq_held(&port->ip_messages);
+
+       /* Watchport boost only works for non-special active ports mapped in an ipc space */
+       if (!ip_active(port) || port->ip_specialreply ||
+           port->ip_receiver_name == MACH_PORT_NULL) {
+               imq_unlock(&port->ip_messages);
+               ip_unlock(port);
+               return KERN_FAILURE;
+       }
+
+       if (port->ip_sync_link_state != PORT_SYNC_LINK_ANY) {
+               /* Sever the linkage if the port was pushing on knote */
+               ipc_port_adjust_sync_link_state_locked(port, PORT_SYNC_LINK_ANY, NULL);
+       }
+
+       *old_elem = ipc_port_update_watchport_elem(port, watchport_elem);
+
+       ipc_port_send_turnstile_recompute_push_locked(port);
+       /* port and mqueue unlocked */
+       return KERN_SUCCESS;
+}
+
+/*
+ *     Routine:        ipc_port_clear_watchport_elem_internal_conditional_locked
+ *     Purpose:
+ *             Remove the turnstile boost of watchport and recompute the push.
+ *     Condition:
+ *             Port locked on entry.
+ *             Port unlocked on return.
+ *     Returns:
+ *             KERN_SUCESS on success.
+ *             KERN_FAILURE otherwise.
+ */
+kern_return_t
+ipc_port_clear_watchport_elem_internal_conditional_locked(
+       ipc_port_t                 port,
+       struct task_watchport_elem *watchport_elem)
+{
+       ip_lock_held(port);
+       imq_held(&port->ip_messages);
+
+       if (ipc_port_watchport_elem(port) != watchport_elem) {
+               imq_unlock(&port->ip_messages);
+               ip_unlock(port);
+               return KERN_FAILURE;
+       }
+
+       ipc_port_clear_watchport_elem_internal(port);
+       ipc_port_send_turnstile_recompute_push_locked(port);
+       /* port and mqueue unlocked */
+       return KERN_SUCCESS;
+}
+
+/*
+ *     Routine:        ipc_port_replace_watchport_elem_conditional_locked
+ *     Purpose:
+ *             Replace the turnstile boost of watchport and recompute the push.
+ *     Condition:
+ *             Port locked on entry.
+ *             Port unlocked on return.
+ *     Returns:
+ *             KERN_SUCESS on success.
+ *             KERN_FAILURE otherwise.
+ */
+kern_return_t
+ipc_port_replace_watchport_elem_conditional_locked(
+       ipc_port_t                 port,
+       struct task_watchport_elem *old_watchport_elem,
+       struct task_watchport_elem *new_watchport_elem)
+{
+       ip_lock_held(port);
+       imq_held(&port->ip_messages);
+
+       if (ipc_port_watchport_elem(port) != old_watchport_elem) {
+               imq_unlock(&port->ip_messages);
+               ip_unlock(port);
+               return KERN_FAILURE;
+       }
+
+       ipc_port_update_watchport_elem(port, new_watchport_elem);
+       ipc_port_send_turnstile_recompute_push_locked(port);
+       /* port and mqueue unlocked */
+       return KERN_SUCCESS;
+}
+
+/*
+ *     Routine:        ipc_port_clear_watchport_elem_internal
+ *     Purpose:
+ *             Remove the turnstile boost of watchport.
+ *     Condition:
+ *             Port locked on entry.
+ *             Port locked on return.
+ *     Returns:
+ *             Old task_watchport_elem returned.
+ */
+struct task_watchport_elem *
+ipc_port_clear_watchport_elem_internal(
+       ipc_port_t                 port)
+{
+       ip_lock_held(port);
+       imq_held(&port->ip_messages);
+
+       return ipc_port_update_watchport_elem(port, NULL);
+}
+
+/*
+ *     Routine:        ipc_port_send_turnstile_recompute_push_locked
+ *     Purpose:
+ *             Update send turnstile inheritor of port and recompute the push.
+ *     Condition:
+ *             Port locked on entry.
+ *             Port unlocked on return.
+ *     Returns:
+ *             None.
+ */
+static void
+ipc_port_send_turnstile_recompute_push_locked(
+       ipc_port_t port)
+{
+       struct turnstile *send_turnstile = port_send_turnstile(port);
+       if (send_turnstile) {
+               turnstile_reference(send_turnstile);
+               ipc_port_send_update_inheritor(port, send_turnstile,
+                   TURNSTILE_IMMEDIATE_UPDATE);
+       }
+       imq_unlock(&port->ip_messages);
+       ip_unlock(port);
+
+       if (send_turnstile) {
+               turnstile_update_inheritor_complete(send_turnstile,
+                   TURNSTILE_INTERLOCK_NOT_HELD);
+               turnstile_deallocate_safe(send_turnstile);
+       }
+}
+
+/*
+ *     Routine:        ipc_port_get_watchport_inheritor
+ *     Purpose:
+ *             Returns inheritor for watchport.
+ *
+ *     Conditions:
+ *             mqueue locked.
+ *     Returns:
+ *             watchport inheritor.
+ */
+static thread_t
+ipc_port_get_watchport_inheritor(
+       ipc_port_t port)
+{
+       imq_held(&port->ip_messages);
+       return ipc_port_watchport_elem(port)->twe_task->watchports->tw_thread;
+}
+
+/*
+ *     Routine:        ipc_port_impcount_delta
+ *     Purpose:
+ *             Adjust only the importance count associated with a port.
+ *             If there are any adjustments to be made to receiver task,
+ *             those are handled elsewhere.
+ *
+ *             For now, be defensive during deductions to make sure the
+ *             impcount for the port doesn't underflow zero.  This will
+ *             go away when the port boost addition is made atomic (see
+ *             note in ipc_port_importance_delta()).
+ *     Conditions:
+ *             The port is referenced and locked.
+ *             Nothing else is locked.
+ */
+mach_port_delta_t
+ipc_port_impcount_delta(
+       ipc_port_t        port,
+       mach_port_delta_t delta,
+       ipc_port_t        __unused base)
+{
+       mach_port_delta_t absdelta;
+
+       if (!ip_active(port)) {
+               return 0;
+       }
+
+       /* adding/doing nothing is easy */
+       if (delta >= 0) {
+               port->ip_impcount += delta;
+               return delta;
+       }
+
+       absdelta = 0 - delta;
+       if (port->ip_impcount >= absdelta) {
+               port->ip_impcount -= absdelta;
+               return delta;
+       }
+
+#if (DEVELOPMENT || DEBUG)
+       if (port->ip_receiver_name != MACH_PORT_NULL) {
+               task_t target_task = port->ip_receiver->is_task;
+               ipc_importance_task_t target_imp = target_task->task_imp_base;
+               const char *target_procname;
+               int target_pid;
+
+               if (target_imp != IIT_NULL) {
+                       target_procname = target_imp->iit_procname;
+                       target_pid = target_imp->iit_bsd_pid;
+               } else {
+                       target_procname = "unknown";
+                       target_pid = -1;
+               }
+               printf("Over-release of importance assertions for port 0x%x receiver pid %d (%s), "
+                   "dropping %d assertion(s) but port only has %d remaining.\n",
+                   port->ip_receiver_name,
+                   target_pid, target_procname,
+                   absdelta, port->ip_impcount);
+       } else if (base != IP_NULL) {
+               task_t target_task = base->ip_receiver->is_task;
+               ipc_importance_task_t target_imp = target_task->task_imp_base;
+               const char *target_procname;
+               int target_pid;
+
+               if (target_imp != IIT_NULL) {
+                       target_procname = target_imp->iit_procname;
+                       target_pid = target_imp->iit_bsd_pid;
+               } else {
+                       target_procname = "unknown";
+                       target_pid = -1;
+               }
+               printf("Over-release of importance assertions for port 0x%lx "
+                   "enqueued on port 0x%x with receiver pid %d (%s), "
+                   "dropping %d assertion(s) but port only has %d remaining.\n",
+                   (unsigned long)VM_KERNEL_UNSLIDE_OR_PERM((uintptr_t)port),
+                   base->ip_receiver_name,
+                   target_pid, target_procname,
+                   absdelta, port->ip_impcount);
+       }
+#endif
+
+       delta = 0 - port->ip_impcount;
+       port->ip_impcount = 0;
+       return delta;
 }
 
 /*
@@ -1318,6 +2230,7 @@ ipc_port_impcount_delta(
  *             and if so, apply the delta.
  *     Conditions:
  *             The port is referenced and locked on entry.
+ *             Importance may be locked.
  *             Nothing else is locked.
  *             The lock may be dropped on exit.
  *             Returns TRUE if lock was dropped.
@@ -1326,17 +2239,21 @@ ipc_port_impcount_delta(
 
 boolean_t
 ipc_port_importance_delta_internal(
-       ipc_port_t              port,
-       mach_port_delta_t       *deltap,
-       ipc_importance_task_t   *imp_task)
+       ipc_port_t              port,
+       natural_t               options,
+       mach_port_delta_t       *deltap,
+       ipc_importance_task_t   *imp_task)
 {
        ipc_port_t next, base;
        boolean_t dropped = FALSE;
 
        *imp_task = IIT_NULL;
 
-       if (*deltap == 0)
+       if (*deltap == 0) {
                return FALSE;
+       }
+
+       assert(options == IPID_OPTION_NORMAL || options == IPID_OPTION_SENDPOSSIBLE);
 
        base = port;
 
@@ -1344,38 +2261,43 @@ ipc_port_importance_delta_internal(
        if (ip_active(port) &&
            port->ip_destination != IP_NULL &&
            port->ip_receiver_name == MACH_PORT_NULL) {
-
                dropped = TRUE;
 
                ip_unlock(port);
                ipc_port_multiple_lock(); /* massive serialization */
                ip_lock(base);
 
-               while(ip_active(base) &&
-                     base->ip_destination != IP_NULL &&
-                     base->ip_receiver_name == MACH_PORT_NULL) {
-
+               while (ip_active(base) &&
+                   base->ip_destination != IP_NULL &&
+                   base->ip_receiver_name == MACH_PORT_NULL) {
                        base = base->ip_destination;
                        ip_lock(base);
                }
                ipc_port_multiple_unlock();
        }
 
-       /* unlock down to the base, adding a boost at each level */
+       /*
+        * If the port lock is dropped b/c the port is in transit, there is a
+        * race window where another thread can drain messages and/or fire a
+        * send possible notification before we get here.
+        *
+        * We solve this race by checking to see if our caller armed the send
+        * possible notification, whether or not it's been fired yet, and
+        * whether or not we've already set the port's ip_spimportant bit. If
+        * we don't need a send-possible boost, then we'll just apply a
+        * harmless 0-boost to the port.
+        */
+       if (options & IPID_OPTION_SENDPOSSIBLE) {
+               assert(*deltap == 1);
+               if (port->ip_sprequests && port->ip_spimportant == 0) {
+                       port->ip_spimportant = 1;
+               } else {
+                       *deltap = 0;
+               }
+       }
+
+       /* unlock down to the base, adjusting boost(s) at each level */
        for (;;) {
-               /*
-                * JMM TODO - because of the port unlock to grab the multiple lock
-                * above, a subsequent drop of importance could race and beat
-                * the "previous" increase - causing the port impcount to go
-                * negative briefly.  The defensive deduction performed by
-                * ipc_port_impcount_delta() defeats that, and therefore can
-                * cause an importance leak once the increase finally arrives.
-                *
-                * Need to rework the importance delta logic to be more like
-                * ipc_importance_inherit_from() where it locks all it needs in
-                * one pass to avoid any lock drops - to keep that race from
-                * ever occuring.
-                */
                *deltap = ipc_port_impcount_delta(port, *deltap, base);
 
                if (port == base) {
@@ -1392,10 +2314,10 @@ ipc_port_importance_delta_internal(
        /* find the task (if any) to boost according to the base */
        if (ip_active(base)) {
                if (base->ip_tempowner != 0) {
-                       if (IIT_NULL != base->ip_imp_task)
+                       if (IIT_NULL != base->ip_imp_task) {
                                *imp_task = base->ip_imp_task;
+                       }
                        /* otherwise don't boost */
-
                } else if (base->ip_receiver_name != MACH_PORT_NULL) {
                        ipc_space_t space = base->ip_receiver;
 
@@ -1443,77 +2365,36 @@ ipc_port_importance_delta_internal(
 
 boolean_t
 ipc_port_importance_delta(
-       ipc_port_t              port,
-       mach_port_delta_t       delta)
+       ipc_port_t              port,
+       natural_t               options,
+       mach_port_delta_t       delta)
 {
        ipc_importance_task_t imp_task = IIT_NULL;
        boolean_t dropped;
 
-       dropped = ipc_port_importance_delta_internal(port, &delta, &imp_task);
+       dropped = ipc_port_importance_delta_internal(port, options, &delta, &imp_task);
 
-       if (IIT_NULL == imp_task)
+       if (IIT_NULL == imp_task || delta == 0) {
                return dropped;
+       }
 
        if (!dropped) {
-               dropped = TRUE;
                ip_unlock(port);
        }
 
        assert(ipc_importance_task_is_any_receiver_type(imp_task));
 
-       if (delta > 0)
+       if (delta > 0) {
                ipc_importance_task_hold_internal_assertion(imp_task, delta);
-       else
+       } else {
                ipc_importance_task_drop_internal_assertion(imp_task, -delta);
+       }
 
        ipc_importance_task_release(imp_task);
-       return dropped;
+       return TRUE;
 }
 #endif /* IMPORTANCE_INHERITANCE */
 
-/*
- *     Routine:        ipc_port_lookup_notify
- *     Purpose:
- *             Make a send-once notify port from a receive right.
- *             Returns IP_NULL if name doesn't denote a receive right.
- *     Conditions:
- *             The space must be locked (read or write) and active.
- *             Being the active space, we can rely on thread server_id
- *             context to give us the proper server level sub-order
- *             within the space.
- */
-
-ipc_port_t
-ipc_port_lookup_notify(
-       ipc_space_t             space,
-       mach_port_name_t        name)
-{
-       ipc_port_t port;
-       ipc_entry_t entry;
-
-       assert(is_active(space));
-
-       entry = ipc_entry_lookup(space, name);
-       if (entry == IE_NULL)
-               return IP_NULL;
-       if ((entry->ie_bits & MACH_PORT_TYPE_RECEIVE) == 0)
-               return IP_NULL;
-
-       __IGNORE_WCASTALIGN(port = (ipc_port_t) entry->ie_object);
-       assert(port != IP_NULL);
-
-       ip_lock(port);
-       assert(ip_active(port));
-       assert(port->ip_receiver_name == name);
-       assert(port->ip_receiver == space);
-
-       ip_reference(port);
-       port->ip_sorights++;
-       ip_unlock(port);
-
-       return port;
-}
-
 /*
  *     Routine:        ipc_port_make_send_locked
  *     Purpose:
@@ -1524,9 +2405,9 @@ ipc_port_lookup_notify(
  */
 ipc_port_t
 ipc_port_make_send_locked(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
-       assert(ip_active(port));
+       require_ip_active(port);
        port->ip_mscount++;
        port->ip_srights++;
        ip_reference(port);
@@ -1541,17 +2422,15 @@ ipc_port_make_send_locked(
 
 ipc_port_t
 ipc_port_make_send(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
-       
-       if (!IP_VALID(port))
+       if (!IP_VALID(port)) {
                return port;
+       }
 
        ip_lock(port);
        if (ip_active(port)) {
-               port->ip_mscount++;
-               port->ip_srights++;
-               ip_reference(port);
+               ipc_port_make_send_locked(port);
                ip_unlock(port);
                return port;
        }
@@ -1559,6 +2438,22 @@ ipc_port_make_send(
        return IP_DEAD;
 }
 
+/*
+ *     Routine:        ipc_port_copy_send_locked
+ *     Purpose:
+ *             Make a naked send right from another naked send right.
+ *     Conditions:
+ *             port locked and active.
+ */
+void
+ipc_port_copy_send_locked(
+       ipc_port_t      port)
+{
+       assert(port->ip_srights > 0);
+       port->ip_srights++;
+       ip_reference(port);
+}
+
 /*
  *     Routine:        ipc_port_copy_send
  *     Purpose:
@@ -1573,22 +2468,21 @@ ipc_port_make_send(
 
 ipc_port_t
 ipc_port_copy_send(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
        ipc_port_t sright;
 
-       if (!IP_VALID(port))
+       if (!IP_VALID(port)) {
                return port;
+       }
 
        ip_lock(port);
        if (ip_active(port)) {
-               assert(port->ip_srights > 0);
-
-               ip_reference(port);
-               port->ip_srights++;
+               ipc_port_copy_send_locked(port);
                sright = port;
-       } else
+       } else {
                sright = IP_DEAD;
+       }
        ip_unlock(port);
 
        return sright;
@@ -1605,26 +2499,28 @@ ipc_port_copy_send(
 
 mach_port_name_t
 ipc_port_copyout_send(
-       ipc_port_t      sright,
-       ipc_space_t     space)
+       ipc_port_t      sright,
+       ipc_space_t     space)
 {
        mach_port_name_t name;
 
        if (IP_VALID(sright)) {
                kern_return_t kr;
 
-               kr = ipc_object_copyout(space, (ipc_object_t) sright,
-                                       MACH_MSG_TYPE_PORT_SEND, TRUE, &name);
+               kr = ipc_object_copyout(space, ip_to_object(sright),
+                   MACH_MSG_TYPE_PORT_SEND, NULL, NULL, &name);
                if (kr != KERN_SUCCESS) {
                        ipc_port_release_send(sright);
 
-                       if (kr == KERN_INVALID_CAPABILITY)
+                       if (kr == KERN_INVALID_CAPABILITY) {
                                name = MACH_PORT_DEAD;
-                       else
+                       } else {
                                name = MACH_PORT_NULL;
+                       }
                }
-       } else
+       } else {
                name = CAST_MACH_PORT_TO_NAME(sright);
+       }
 
        return name;
 }
@@ -1640,17 +2536,22 @@ ipc_port_copyout_send(
 
 void
 ipc_port_release_send(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
        ipc_port_t nsrequest = IP_NULL;
        mach_port_mscount_t mscount;
 
-       if (!IP_VALID(port))
+       if (!IP_VALID(port)) {
                return;
+       }
 
        ip_lock(port);
 
        assert(port->ip_srights > 0);
+       if (port->ip_srights == 0) {
+               panic("Over-release of port %p send right!", port);
+       }
+
        port->ip_srights--;
 
        if (!ip_active(port)) {
@@ -1683,9 +2584,9 @@ ipc_port_release_send(
 
 ipc_port_t
 ipc_port_make_sonce_locked(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
-       assert(ip_active(port));
+       require_ip_active(port);
        port->ip_sorights++;
        ip_reference(port);
        return port;
@@ -1701,15 +2602,15 @@ ipc_port_make_sonce_locked(
 
 ipc_port_t
 ipc_port_make_sonce(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
-       if (!IP_VALID(port))
+       if (!IP_VALID(port)) {
                return port;
+       }
 
        ip_lock(port);
        if (ip_active(port)) {
-               port->ip_sorights++;
-               ip_reference(port);
+               ipc_port_make_sonce_locked(port);
                ip_unlock(port);
                return port;
        }
@@ -1733,14 +2634,20 @@ ipc_port_make_sonce(
 
 void
 ipc_port_release_sonce(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
-       if (!IP_VALID(port))
+       if (!IP_VALID(port)) {
                return;
+       }
+
+       ipc_port_adjust_special_reply_port(port, IPC_PORT_ADJUST_RESET_BOOSTRAP_CHECKIN);
 
        ip_lock(port);
 
        assert(port->ip_sorights > 0);
+       if (port->ip_sorights == 0) {
+               panic("Over-release of port %p send-once right!", port);
+       }
 
        port->ip_sorights--;
 
@@ -1759,22 +2666,25 @@ ipc_port_release_sonce(
 
 void
 ipc_port_release_receive(
-       ipc_port_t      port)
+       ipc_port_t      port)
 {
        ipc_port_t dest;
 
-       if (!IP_VALID(port))
+       if (!IP_VALID(port)) {
                return;
+       }
 
        ip_lock(port);
-       assert(ip_active(port));
+       require_ip_active(port);
        assert(port->ip_receiver_name == MACH_PORT_NULL);
        dest = port->ip_destination;
 
        ipc_port_destroy(port); /* consumes ref, unlocks */
 
-       if (dest != IP_NULL)
+       if (dest != IP_NULL) {
+               ipc_port_send_turnstile_complete(dest);
                ip_release(dest);
+       }
 }
 
 /*
@@ -1789,29 +2699,31 @@ ipc_port_release_receive(
 
 ipc_port_t
 ipc_port_alloc_special(
-       ipc_space_t     space)
+       ipc_space_t             space,
+       ipc_port_init_flags_t   flags)
 {
        ipc_port_t port;
 
-       __IGNORE_WCASTALIGN(port = (ipc_port_t) io_alloc(IOT_PORT));
-       if (port == IP_NULL)
+       port = ip_object_to_port(io_alloc(IOT_PORT));
+       if (port == IP_NULL) {
                return IP_NULL;
+       }
 
 #if     MACH_ASSERT
        uintptr_t buf[IP_CALLSTACK_MAX];
        ipc_port_callstack_init_debug(&buf[0], IP_CALLSTACK_MAX);
-#endif /* MACH_ASSERT */       
+#endif /* MACH_ASSERT */
 
        bzero((char *)port, sizeof(*port));
-       io_lock_init(&port->ip_object);
+       io_lock_init(ip_to_object(port));
        port->ip_references = 1;
        port->ip_object.io_bits = io_makebits(TRUE, IOT_PORT, 0);
 
-       ipc_port_init(port, space, 1);
+       ipc_port_init(port, space, flags, 1);
 
 #if     MACH_ASSERT
        ipc_port_init_debug(port, &buf[0], IP_CALLSTACK_MAX);
-#endif  /* MACH_ASSERT */              
+#endif  /* MACH_ASSERT */
 
        return port;
 }
@@ -1827,11 +2739,11 @@ ipc_port_alloc_special(
 
 void
 ipc_port_dealloc_special(
-       ipc_port_t                      port,
-       __assert_only ipc_space_t       space)
+       ipc_port_t                      port,
+       __assert_only ipc_space_t       space)
 {
        ip_lock(port);
-       assert(ip_active(port));
+       require_ip_active(port);
 //     assert(port->ip_receiver_name != MACH_PORT_NULL);
        assert(port->ip_receiver == space);
 
@@ -1840,11 +2752,13 @@ ipc_port_dealloc_special(
         *      the ipc_space_kernel check in ipc_mqueue_send.
         */
 
+       imq_lock(&port->ip_messages);
        port->ip_receiver_name = MACH_PORT_NULL;
        port->ip_receiver = IS_NULL;
+       imq_unlock(&port->ip_messages);
 
        /* relevant part of ipc_port_clear_receiver */
-       ipc_port_set_mscount(port, 0);
+       port->ip_mscount = 0;
        port->ip_messages.imq_seqno = 0;
 
        ipc_port_destroy(port);
@@ -1861,11 +2775,19 @@ ipc_port_dealloc_special(
  */
 void
 ipc_port_finalize(
-       ipc_port_t              port)
+       ipc_port_t              port)
 {
        ipc_port_request_t requests = port->ip_requests;
 
-       assert(!ip_active(port));
+       assert(port_send_turnstile(port) == TURNSTILE_NULL);
+       if (imq_is_turnstile_proxy(&port->ip_messages)) {
+               assert(ipc_port_rcv_turnstile(port) == TURNSTILE_NULL);
+       }
+
+       if (ip_active(port)) {
+               panic("Trying to free an active port. port %p", port);
+       }
+
        if (requests != IPR_NULL) {
                ipc_table_size_t its = requests->ipr_size;
                it_requests_free(its, requests);
@@ -1873,13 +2795,129 @@ ipc_port_finalize(
        }
 
        ipc_mqueue_deinit(&port->ip_messages);
-       
-#if    MACH_ASSERT
+
+#if     MACH_ASSERT
        ipc_port_track_dealloc(port);
-#endif /* MACH_ASSERT */
+#endif  /* MACH_ASSERT */
 }
 
-#if    MACH_ASSERT
+/*
+ *     Routine:        kdp_mqueue_send_find_owner
+ *     Purpose:
+ *             Discover the owner of the ipc_mqueue that contains the input
+ *             waitq object. The thread blocked on the waitq should be
+ *             waiting for an IPC_MQUEUE_FULL event.
+ *     Conditions:
+ *             The 'waitinfo->wait_type' value should already be set to
+ *             kThreadWaitPortSend.
+ *     Note:
+ *             If we find out that the containing port is actually in
+ *             transit, we reset the wait_type field to reflect this.
+ */
+void
+kdp_mqueue_send_find_owner(struct waitq * waitq, __assert_only event64_t event, thread_waitinfo_t * waitinfo)
+{
+       struct turnstile *turnstile;
+       assert(waitinfo->wait_type == kThreadWaitPortSend);
+       assert(event == IPC_MQUEUE_FULL);
+       assert(waitq_is_turnstile_queue(waitq));
+
+       turnstile = waitq_to_turnstile(waitq);
+       ipc_port_t port = (ipc_port_t)turnstile->ts_proprietor; /* we are blocking on send */
+       assert(kdp_is_in_zone(port, "ipc ports"));
+
+       waitinfo->owner = 0;
+       waitinfo->context  = VM_KERNEL_UNSLIDE_OR_PERM(port);
+       if (ip_lock_held_kdp(port)) {
+               /*
+                * someone has the port locked: it may be in an
+                * inconsistent state: bail
+                */
+               waitinfo->owner = STACKSHOT_WAITOWNER_PORT_LOCKED;
+               return;
+       }
+
+       if (ip_active(port)) {
+               if (port->ip_tempowner) {
+                       if (port->ip_imp_task != IIT_NULL && port->ip_imp_task->iit_task != NULL) {
+                               /* port is held by a tempowner */
+                               waitinfo->owner = pid_from_task(port->ip_imp_task->iit_task);
+                       } else {
+                               waitinfo->owner = STACKSHOT_WAITOWNER_INTRANSIT;
+                       }
+               } else if (port->ip_receiver_name) {
+                       /* port in a space */
+                       if (port->ip_receiver == ipc_space_kernel) {
+                               /*
+                                * The kernel pid is 0, make this
+                                * distinguishable from no-owner and
+                                * inconsistent port state.
+                                */
+                               waitinfo->owner = STACKSHOT_WAITOWNER_KERNEL;
+                       } else {
+                               waitinfo->owner = pid_from_task(port->ip_receiver->is_task);
+                       }
+               } else if (port->ip_destination != IP_NULL) {
+                       /* port in transit */
+                       waitinfo->wait_type = kThreadWaitPortSendInTransit;
+                       waitinfo->owner     = VM_KERNEL_UNSLIDE_OR_PERM(port->ip_destination);
+               }
+       }
+}
+
+/*
+ *     Routine:        kdp_mqueue_recv_find_owner
+ *     Purpose:
+ *             Discover the "owner" of the ipc_mqueue that contains the input
+ *             waitq object. The thread blocked on the waitq is trying to
+ *             receive on the mqueue.
+ *     Conditions:
+ *             The 'waitinfo->wait_type' value should already be set to
+ *             kThreadWaitPortReceive.
+ *     Note:
+ *             If we find that we are actualy waiting on a port set, we reset
+ *             the wait_type field to reflect this.
+ */
+void
+kdp_mqueue_recv_find_owner(struct waitq * waitq, __assert_only event64_t event, thread_waitinfo_t * waitinfo)
+{
+       assert(waitinfo->wait_type == kThreadWaitPortReceive);
+       assert(event == IPC_MQUEUE_RECEIVE);
+
+       ipc_mqueue_t mqueue = imq_from_waitq(waitq);
+       waitinfo->owner     = 0;
+       if (imq_is_set(mqueue)) { /* we are waiting on a port set */
+               ipc_pset_t set = ips_from_mq(mqueue);
+               assert(kdp_is_in_zone(set, "ipc port sets"));
+
+               /* Reset wait type to specify waiting on port set receive */
+               waitinfo->wait_type = kThreadWaitPortSetReceive;
+               waitinfo->context   = VM_KERNEL_UNSLIDE_OR_PERM(set);
+               if (ips_lock_held_kdp(set)) {
+                       waitinfo->owner = STACKSHOT_WAITOWNER_PSET_LOCKED;
+               }
+               /* There is no specific owner "at the other end" of a port set, so leave unset. */
+       } else {
+               ipc_port_t port   = ip_from_mq(mqueue);
+               assert(kdp_is_in_zone(port, "ipc ports"));
+
+               waitinfo->context = VM_KERNEL_UNSLIDE_OR_PERM(port);
+               if (ip_lock_held_kdp(port)) {
+                       waitinfo->owner = STACKSHOT_WAITOWNER_PORT_LOCKED;
+                       return;
+               }
+
+               if (ip_active(port)) {
+                       if (port->ip_receiver_name != MACH_PORT_NULL) {
+                               waitinfo->owner = port->ip_receiver_name;
+                       } else {
+                               waitinfo->owner = STACKSHOT_WAITOWNER_INTRANSIT;
+                       }
+               }
+       }
+}
+
+#if     MACH_ASSERT
 #include <kern/machine.h>
 
 /*
@@ -1888,23 +2926,23 @@ ipc_port_finalize(
  *     deallocation is intercepted via io_free.
  */
 #if 0
-queue_head_t   port_alloc_queue;
-lck_spin_t     port_alloc_queue_lock;
+queue_head_t    port_alloc_queue;
+lck_spin_t      port_alloc_queue_lock;
 #endif
 
-unsigned long  port_count = 0;
-unsigned long  port_count_warning = 20000;
-unsigned long  port_timestamp = 0;
+unsigned long   port_count = 0;
+unsigned long   port_count_warning = 20000;
+unsigned long   port_timestamp = 0;
 
-void           db_port_stack_trace(
-                       ipc_port_t      port);
-void           db_ref(
-                       int             refs);
-int            db_port_walk(
-                       unsigned int    verbose,
-                       unsigned int    display,
-                       unsigned int    ref_search,
-                       unsigned int    ref_target);
+void            db_port_stack_trace(
+       ipc_port_t      port);
+void            db_ref(
+       int             refs);
+int             db_port_walk(
+       unsigned int    verbose,
+       unsigned int    display,
+       unsigned int    ref_search,
+       unsigned int    ref_target);
 
 /*
  *     Initialize global state needed for run-time
@@ -1918,8 +2956,9 @@ ipc_port_debug_init(void)
        lck_spin_init(&port_alloc_queue_lock, &ipc_lck_grp, &ipc_lck_attr);
 #endif
 
-       if (!PE_parse_boot_argn("ipc_portbt", &ipc_portbt, sizeof (ipc_portbt)))
+       if (!PE_parse_boot_argn("ipc_portbt", &ipc_portbt, sizeof(ipc_portbt))) {
                ipc_portbt = 0;
+       }
 }
 
 #ifdef MACH_BSD
@@ -1932,33 +2971,37 @@ extern int proc_pid(struct proc*);
  */
 void
 ipc_port_init_debug(
-       ipc_port_t      port,
-       uintptr_t       *callstack,
-       unsigned int    callstack_max)
+       ipc_port_t      port,
+       uintptr_t       *callstack,
+       unsigned int    callstack_max)
 {
-       unsigned int    i;
+       unsigned int    i;
 
        port->ip_thread = current_thread();
        port->ip_timetrack = port_timestamp++;
-       for (i = 0; i < callstack_max; ++i)
-               port->ip_callstack[i] = callstack[i];   
-       for (i = 0; i < IP_NSPARES; ++i)
-               port->ip_spares[i] = 0; 
+       for (i = 0; i < callstack_max; ++i) {
+               port->ip_callstack[i] = callstack[i];
+       }
+       for (i = 0; i < IP_NSPARES; ++i) {
+               port->ip_spares[i] = 0;
+       }
 
 #ifdef MACH_BSD
        task_t task = current_task();
        if (task != TASK_NULL) {
                struct proc* proc = (struct proc*) get_bsdtask_info(task);
-               if (proc)
+               if (proc) {
                        port->ip_spares[0] = proc_pid(proc);
+               }
        }
 #endif /* MACH_BSD */
 
 #if 0
        lck_spin_lock(&port_alloc_queue_lock);
        ++port_count;
-       if (port_count_warning > 0 && port_count >= port_count_warning)
+       if (port_count_warning > 0 && port_count >= port_count_warning) {
                assert(port_count < port_count_warning);
+       }
        queue_enter(&port_alloc_queue, port, ipc_port_t, ip_port_links);
        lck_spin_unlock(&port_alloc_queue_lock);
 #endif
@@ -1975,17 +3018,19 @@ ipc_port_init_debug(
  */
 void
 ipc_port_callstack_init_debug(
-       uintptr_t       *callstack,
-       unsigned int    callstack_max)
+       uintptr_t       *callstack,
+       unsigned int    callstack_max)
 {
-       unsigned int    i;
+       unsigned int    i;
 
        /* guarantee the callstack is initialized */
-       for (i=0; i < callstack_max; i++)
-               callstack[i] = 0;       
+       for (i = 0; i < callstack_max; i++) {
+               callstack[i] = 0;
+       }
 
-       if (ipc_portbt)
+       if (ipc_portbt) {
                machine_callstack(callstack, callstack_max);
+       }
 }
 
 /*
@@ -1996,13 +3041,13 @@ ipc_port_callstack_init_debug(
 #if 1
 void
 ipc_port_track_dealloc(
-       __unused ipc_port_t     port)
+       __unused ipc_port_t     port)
 {
 }
 #else
 void
 ipc_port_track_dealloc(
-       ipc_port_t              port)
+       ipc_port_t              port)
 {
        lck_spin_lock(&port_alloc_queue_lock);
        assert(port_count > 0);
@@ -2013,4 +3058,4 @@ ipc_port_track_dealloc(
 #endif
 
 
-#endif /* MACH_ASSERT */
+#endif  /* MACH_ASSERT */