xnu-7195.60.75.tar.gz

[apple/xnu.git] / osfmk / kern / sync_sema.c

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 *
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 * 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
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
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 * Please obtain a copy of the License at
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/*
 * @OSF_COPYRIGHT@
 *
 */
/*
 *      File:   kern/sync_sema.c
 *      Author: Joseph CaraDonna
 *
 *      Contains RT distributed semaphore synchronization services.
 */

#include <mach/mach_types.h>
#include <mach/mach_traps.h>
#include <mach/kern_return.h>
#include <mach/semaphore.h>
#include <mach/sync_policy.h>
#include <mach/task.h>

#include <kern/misc_protos.h>
#include <kern/sync_sema.h>
#include <kern/spl.h>
#include <kern/ipc_kobject.h>
#include <kern/ipc_sync.h>
#include <kern/ipc_tt.h>
#include <kern/thread.h>
#include <kern/clock.h>
#include <ipc/ipc_port.h>
#include <ipc/ipc_space.h>
#include <kern/host.h>
#include <kern/waitq.h>
#include <kern/zalloc.h>
#include <kern/mach_param.h>

#include <libkern/OSAtomic.h>

static unsigned int semaphore_event;
#define SEMAPHORE_EVENT CAST_EVENT64_T(&semaphore_event)

ZONE_DECLARE(semaphore_zone, "semaphores", sizeof(struct semaphore), ZC_NONE);

os_refgrp_decl(static, sema_refgrp, "semaphore", NULL);

/* Forward declarations */


kern_return_t
semaphore_wait_trap_internal(
        mach_port_name_t name,
        void (*caller_cont)(kern_return_t));

kern_return_t
semaphore_wait_signal_trap_internal(
        mach_port_name_t wait_name,
        mach_port_name_t signal_name,
        void (*caller_cont)(kern_return_t));

kern_return_t
semaphore_timedwait_trap_internal(
        mach_port_name_t name,
        unsigned int sec,
        clock_res_t nsec,
        void (*caller_cont)(kern_return_t));

kern_return_t
semaphore_timedwait_signal_trap_internal(
        mach_port_name_t wait_name,
        mach_port_name_t signal_name,
        unsigned int sec,
        clock_res_t nsec,
        void (*caller_cont)(kern_return_t));

kern_return_t
semaphore_signal_internal_trap(mach_port_name_t sema_name);

kern_return_t
semaphore_signal_internal(
        semaphore_t             semaphore,
        thread_t                        thread,
        int                             options);

kern_return_t
semaphore_convert_wait_result(
        int                             wait_result);

void
semaphore_wait_continue(void *arg __unused, wait_result_t wr);

static kern_return_t
semaphore_wait_internal(
        semaphore_t             wait_semaphore,
        semaphore_t             signal_semaphore,
        uint64_t                deadline,
        int                             option,
        void (*caller_cont)(kern_return_t));

static __inline__ uint64_t
semaphore_deadline(
        unsigned int            sec,
        clock_res_t                     nsec)
{
        uint64_t        abstime;

        nanoseconds_to_absolutetime((uint64_t)sec *     NSEC_PER_SEC + nsec, &abstime);
        clock_absolutetime_interval_to_deadline(abstime, &abstime);

        return abstime;
}

/*
 *      Routine:        semaphore_create
 *
 *      Creates a semaphore.
 *      The port representing the semaphore is returned as a parameter.
 */
kern_return_t
semaphore_create(
        task_t                  task,
        semaphore_t             *new_semaphore,
        int                     policy,
        int                     value)
{
        semaphore_t             s = SEMAPHORE_NULL;
        kern_return_t           kret;

        *new_semaphore = SEMAPHORE_NULL;
        if (task == TASK_NULL || value < 0 || policy > SYNC_POLICY_MAX || policy < 0) {
                return KERN_INVALID_ARGUMENT;
        }

        s = (semaphore_t) zalloc(semaphore_zone);

        if (s == SEMAPHORE_NULL) {
                return KERN_RESOURCE_SHORTAGE;
        }

        kret = waitq_init(&s->waitq, policy | SYNC_POLICY_DISABLE_IRQ); /* also inits lock */
        if (kret != KERN_SUCCESS) {
                zfree(semaphore_zone, s);
                return kret;
        }

        /*
         * Initialize the semaphore values.
         */
        s->port = IP_NULL;
        os_ref_init(&s->ref_count, &sema_refgrp);
        s->count = value;
        s->active = TRUE;
        s->owner = task;

        /*
         *  Associate the new semaphore with the task by adding
         *  the new semaphore to the task's semaphore list.
         */
        task_lock(task);
        enqueue_head(&task->semaphore_list, (queue_entry_t) s);
        task->semaphores_owned++;
        task_unlock(task);

        *new_semaphore = s;

        return KERN_SUCCESS;
}

/*
 *      Routine:        semaphore_destroy_internal
 *
 *      Disassociate a semaphore from its owning task, mark it inactive,
 *      and set any waiting threads running with THREAD_RESTART.
 *
 *      Conditions:
 *                      task is locked
 *                      semaphore is locked
 *                      semaphore is owned by the specified task
 *      Returns:
 *                      with semaphore unlocked
 */
static void
semaphore_destroy_internal(
        task_t                  task,
        semaphore_t             semaphore)
{
        int                     old_count;

        /* unlink semaphore from owning task */
        assert(semaphore->owner == task);
        remqueue((queue_entry_t) semaphore);
        semaphore->owner = TASK_NULL;
        task->semaphores_owned--;

        /*
         *  Deactivate semaphore
         */
        assert(semaphore->active);
        semaphore->active = FALSE;

        /*
         *  Wakeup blocked threads
         */
        old_count = semaphore->count;
        semaphore->count = 0;

        if (old_count < 0) {
                waitq_wakeup64_all_locked(&semaphore->waitq,
                    SEMAPHORE_EVENT,
                    THREAD_RESTART, NULL,
                    WAITQ_ALL_PRIORITIES,
                    WAITQ_UNLOCK);
                /* waitq/semaphore is unlocked */
        } else {
                semaphore_unlock(semaphore);
        }
}

/*
 *      Routine:        semaphore_destroy
 *
 *      Destroys a semaphore and consume the caller's reference on the
 *      semaphore.
 */
kern_return_t
semaphore_destroy(
        task_t                  task,
        semaphore_t             semaphore)
{
        spl_t spl_level;

        if (semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        if (task == TASK_NULL) {
                semaphore_dereference(semaphore);
                return KERN_INVALID_ARGUMENT;
        }

        task_lock(task);
        spl_level = splsched();
        semaphore_lock(semaphore);

        if (semaphore->owner != task) {
                semaphore_unlock(semaphore);
                semaphore_dereference(semaphore);
                splx(spl_level);
                task_unlock(task);
                return KERN_INVALID_ARGUMENT;
        }

        semaphore_destroy_internal(task, semaphore);
        /* semaphore unlocked */

        splx(spl_level);
        task_unlock(task);

        semaphore_dereference(semaphore);
        return KERN_SUCCESS;
}

/*
 *      Routine:        semaphore_destroy_all
 *
 *      Destroy all the semaphores associated with a given task.
 */
#define SEMASPERSPL 20  /* max number of semaphores to destroy per spl hold */

void
semaphore_destroy_all(
        task_t                  task)
{
        uint32_t count;
        spl_t spl_level;

        count = 0;
        task_lock(task);
        while (!queue_empty(&task->semaphore_list)) {
                semaphore_t semaphore;

                semaphore = (semaphore_t) queue_first(&task->semaphore_list);

                if (count == 0) {
                        spl_level = splsched();
                }
                semaphore_lock(semaphore);

                semaphore_destroy_internal(task, semaphore);
                /* semaphore unlocked */

                /* throttle number of semaphores per interrupt disablement */
                if (++count == SEMASPERSPL) {
                        count = 0;
                        splx(spl_level);
                }
        }
        if (count != 0) {
                splx(spl_level);
        }

        task_unlock(task);
}

/*
 *      Routine:        semaphore_signal_internal
 *
 *              Signals the semaphore as direct.
 *      Assumptions:
 *              Semaphore is locked.
 */
kern_return_t
semaphore_signal_internal(
        semaphore_t             semaphore,
        thread_t                thread,
        int                             options)
{
        kern_return_t kr;
        spl_t  spl_level;

        spl_level = splsched();
        semaphore_lock(semaphore);

        if (!semaphore->active) {
                semaphore_unlock(semaphore);
                splx(spl_level);
                return KERN_TERMINATED;
        }

        if (thread != THREAD_NULL) {
                if (semaphore->count < 0) {
                        kr = waitq_wakeup64_thread_locked(
                                &semaphore->waitq,
                                SEMAPHORE_EVENT,
                                thread,
                                THREAD_AWAKENED,
                                WAITQ_UNLOCK);
                        /* waitq/semaphore is unlocked */
                } else {
                        kr = KERN_NOT_WAITING;
                        semaphore_unlock(semaphore);
                }
                splx(spl_level);
                return kr;
        }

        if (options & SEMAPHORE_SIGNAL_ALL) {
                int old_count = semaphore->count;

                kr = KERN_NOT_WAITING;
                if (old_count < 0) {
                        semaphore->count = 0;  /* always reset */
                        kr = waitq_wakeup64_all_locked(
                                &semaphore->waitq,
                                SEMAPHORE_EVENT,
                                THREAD_AWAKENED, NULL,
                                WAITQ_ALL_PRIORITIES,
                                WAITQ_UNLOCK);
                        /* waitq / semaphore is unlocked */
                } else {
                        if (options & SEMAPHORE_SIGNAL_PREPOST) {
                                semaphore->count++;
                        }
                        kr = KERN_SUCCESS;
                        semaphore_unlock(semaphore);
                }
                splx(spl_level);
                return kr;
        }

        if (semaphore->count < 0) {
                waitq_options_t wq_option = (options & SEMAPHORE_THREAD_HANDOFF) ?
                    WQ_OPTION_HANDOFF : WQ_OPTION_NONE;
                kr = waitq_wakeup64_one_locked(
                        &semaphore->waitq,
                        SEMAPHORE_EVENT,
                        THREAD_AWAKENED, NULL,
                        WAITQ_ALL_PRIORITIES,
                        WAITQ_KEEP_LOCKED,
                        wq_option);
                if (kr == KERN_SUCCESS) {
                        semaphore_unlock(semaphore);
                        splx(spl_level);
                        return KERN_SUCCESS;
                } else {
                        semaphore->count = 0;  /* all waiters gone */
                }
        }

        if (options & SEMAPHORE_SIGNAL_PREPOST) {
                semaphore->count++;
        }

        semaphore_unlock(semaphore);
        splx(spl_level);
        return KERN_NOT_WAITING;
}

/*
 *      Routine:        semaphore_signal_thread
 *
 *      If the specified thread is blocked on the semaphore, it is
 *      woken up.  If a NULL thread was supplied, then any one
 *      thread is woken up.  Otherwise the caller gets KERN_NOT_WAITING
 *      and the semaphore is unchanged.
 */
kern_return_t
semaphore_signal_thread(
        semaphore_t     semaphore,
        thread_t        thread)
{
        kern_return_t           ret;

        if (semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        ret = semaphore_signal_internal(semaphore,
            thread,
            SEMAPHORE_OPTION_NONE);
        return ret;
}

/*
 *      Routine:        semaphore_signal_thread_trap
 *
 *      Trap interface to the semaphore_signal_thread function.
 */
kern_return_t
semaphore_signal_thread_trap(
        struct semaphore_signal_thread_trap_args *args)
{
        mach_port_name_t sema_name = args->signal_name;
        mach_port_name_t thread_name = args->thread_name;
        semaphore_t     semaphore;
        thread_t        thread;
        kern_return_t   kr;

        /*
         * MACH_PORT_NULL is not an error. It means that we want to
         * select any one thread that is already waiting, but not to
         * pre-post the semaphore.
         */
        if (thread_name != MACH_PORT_NULL) {
                thread = port_name_to_thread(thread_name, PORT_TO_THREAD_NONE);
                if (thread == THREAD_NULL) {
                        return KERN_INVALID_ARGUMENT;
                }
        } else {
                thread = THREAD_NULL;
        }

        kr = port_name_to_semaphore(sema_name, &semaphore);
        if (kr == KERN_SUCCESS) {
                kr = semaphore_signal_internal(semaphore,
                    thread,
                    SEMAPHORE_OPTION_NONE);
                semaphore_dereference(semaphore);
        }
        if (thread != THREAD_NULL) {
                thread_deallocate(thread);
        }
        return kr;
}



/*
 *      Routine:        semaphore_signal
 *
 *              Traditional (in-kernel client and MIG interface) semaphore
 *              signal routine.  Most users will access the trap version.
 *
 *              This interface in not defined to return info about whether
 *              this call found a thread waiting or not.  The internal
 *              routines (and future external routines) do.  We have to
 *              convert those into plain KERN_SUCCESS returns.
 */
kern_return_t
semaphore_signal(
        semaphore_t             semaphore)
{
        kern_return_t           kr;

        if (semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        kr = semaphore_signal_internal(semaphore,
            THREAD_NULL,
            SEMAPHORE_SIGNAL_PREPOST);
        if (kr == KERN_NOT_WAITING) {
                return KERN_SUCCESS;
        }
        return kr;
}

/*
 *      Routine:        semaphore_signal_trap
 *
 *      Trap interface to the semaphore_signal function.
 */
kern_return_t
semaphore_signal_trap(
        struct semaphore_signal_trap_args *args)
{
        mach_port_name_t sema_name = args->signal_name;

        return semaphore_signal_internal_trap(sema_name);
}

kern_return_t
semaphore_signal_internal_trap(mach_port_name_t sema_name)
{
        semaphore_t     semaphore;
        kern_return_t kr;

        kr = port_name_to_semaphore(sema_name, &semaphore);
        if (kr == KERN_SUCCESS) {
                kr = semaphore_signal_internal(semaphore,
                    THREAD_NULL,
                    SEMAPHORE_SIGNAL_PREPOST);
                semaphore_dereference(semaphore);
                if (kr == KERN_NOT_WAITING) {
                        kr = KERN_SUCCESS;
                }
        }
        return kr;
}

/*
 *      Routine:        semaphore_signal_all
 *
 *      Awakens ALL threads currently blocked on the semaphore.
 *      The semaphore count returns to zero.
 */
kern_return_t
semaphore_signal_all(
        semaphore_t             semaphore)
{
        kern_return_t kr;

        if (semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        kr = semaphore_signal_internal(semaphore,
            THREAD_NULL,
            SEMAPHORE_SIGNAL_ALL);
        if (kr == KERN_NOT_WAITING) {
                return KERN_SUCCESS;
        }
        return kr;
}

/*
 *      Routine:        semaphore_signal_all_trap
 *
 *      Trap interface to the semaphore_signal_all function.
 */
kern_return_t
semaphore_signal_all_trap(
        struct semaphore_signal_all_trap_args *args)
{
        mach_port_name_t sema_name = args->signal_name;
        semaphore_t     semaphore;
        kern_return_t kr;

        kr = port_name_to_semaphore(sema_name, &semaphore);
        if (kr == KERN_SUCCESS) {
                kr = semaphore_signal_internal(semaphore,
                    THREAD_NULL,
                    SEMAPHORE_SIGNAL_ALL);
                semaphore_dereference(semaphore);
                if (kr == KERN_NOT_WAITING) {
                        kr = KERN_SUCCESS;
                }
        }
        return kr;
}

/*
 *      Routine:        semaphore_convert_wait_result
 *
 *      Generate the return code after a semaphore wait/block.  It
 *      takes the wait result as an input and coverts that to an
 *      appropriate result.
 */
kern_return_t
semaphore_convert_wait_result(int wait_result)
{
        switch (wait_result) {
        case THREAD_AWAKENED:
                return KERN_SUCCESS;

        case THREAD_TIMED_OUT:
                return KERN_OPERATION_TIMED_OUT;

        case THREAD_INTERRUPTED:
                return KERN_ABORTED;

        case THREAD_RESTART:
                return KERN_TERMINATED;

        default:
                panic("semaphore_block\n");
                return KERN_FAILURE;
        }
}

/*
 *      Routine:        semaphore_wait_continue
 *
 *      Common continuation routine after waiting on a semphore.
 *      It returns directly to user space.
 */
void
semaphore_wait_continue(void *arg __unused, wait_result_t wr)
{
        thread_t self = current_thread();
        void (*caller_cont)(kern_return_t) = self->sth_continuation;

        assert(self->sth_waitsemaphore != SEMAPHORE_NULL);
        semaphore_dereference(self->sth_waitsemaphore);
        if (self->sth_signalsemaphore != SEMAPHORE_NULL) {
                semaphore_dereference(self->sth_signalsemaphore);
        }

        assert(self->handoff_thread == THREAD_NULL);
        assert(caller_cont != (void (*)(kern_return_t))0);
        (*caller_cont)(semaphore_convert_wait_result(wr));
}

/*
 *      Routine:        semaphore_wait_internal
 *
 *              Decrements the semaphore count by one.  If the count is
 *              negative after the decrement, the calling thread blocks
 *              (possibly at a continuation and/or with a timeout).
 *
 *      Assumptions:
 *              The reference
 *              A reference is held on the signal semaphore.
 */
static kern_return_t
semaphore_wait_internal(
        semaphore_t             wait_semaphore,
        semaphore_t             signal_semaphore,
        uint64_t                deadline,
        int                             option,
        void                    (*caller_cont)(kern_return_t))
{
        int                                     wait_result;
        spl_t                           spl_level;
        kern_return_t           kr = KERN_ALREADY_WAITING;

        spl_level = splsched();
        semaphore_lock(wait_semaphore);
        thread_t self = current_thread();
        thread_t handoff_thread = THREAD_NULL;
        thread_handoff_option_t handoff_option = THREAD_HANDOFF_NONE;
        int semaphore_signal_options = SEMAPHORE_SIGNAL_PREPOST;

        if (!wait_semaphore->active) {
                kr = KERN_TERMINATED;
        } else if (wait_semaphore->count > 0) {
                wait_semaphore->count--;
                kr = KERN_SUCCESS;
        } else if (option & SEMAPHORE_TIMEOUT_NOBLOCK) {
                kr = KERN_OPERATION_TIMED_OUT;
        } else {
                wait_semaphore->count = -1;  /* we don't keep an actual count */

                thread_set_pending_block_hint(self, kThreadWaitSemaphore);
                (void)waitq_assert_wait64_locked(
                        &wait_semaphore->waitq,
                        SEMAPHORE_EVENT,
                        THREAD_ABORTSAFE,
                        TIMEOUT_URGENCY_USER_NORMAL,
                        deadline, TIMEOUT_NO_LEEWAY,
                        self);

                semaphore_signal_options |= SEMAPHORE_THREAD_HANDOFF;
        }
        semaphore_unlock(wait_semaphore);
        splx(spl_level);

        /*
         * wait_semaphore is unlocked so we are free to go ahead and
         * signal the signal_semaphore (if one was provided).
         */
        if (signal_semaphore != SEMAPHORE_NULL) {
                kern_return_t signal_kr;

                /*
                 * lock the signal semaphore reference we got and signal it.
                 * This will NOT block (we cannot block after having asserted
                 * our intention to wait above).
                 */
                signal_kr = semaphore_signal_internal(signal_semaphore,
                    THREAD_NULL, semaphore_signal_options);

                if (signal_kr == KERN_NOT_WAITING) {
                        assert(self->handoff_thread == THREAD_NULL);
                        signal_kr = KERN_SUCCESS;
                } else if (signal_kr == KERN_TERMINATED) {
                        /*
                         * Uh!Oh!  The semaphore we were to signal died.
                         * We have to get ourselves out of the wait in
                         * case we get stuck here forever (it is assumed
                         * that the semaphore we were posting is gating
                         * the decision by someone else to post the
                         * semaphore we are waiting on).  People will
                         * discover the other dead semaphore soon enough.
                         * If we got out of the wait cleanly (someone
                         * already posted a wakeup to us) then return that
                         * (most important) result.  Otherwise,
                         * return the KERN_TERMINATED status.
                         */
                        assert(self->handoff_thread == THREAD_NULL);
                        clear_wait(self, THREAD_INTERRUPTED);
                        kr = semaphore_convert_wait_result(self->wait_result);
                        if (kr == KERN_ABORTED) {
                                kr = KERN_TERMINATED;
                        }
                }
        }

        /*
         * If we had an error, or we didn't really need to wait we can
         * return now that we have signalled the signal semaphore.
         */
        if (kr != KERN_ALREADY_WAITING) {
                assert(self->handoff_thread == THREAD_NULL);
                return kr;
        }

        if (self->handoff_thread) {
                handoff_thread = self->handoff_thread;
                self->handoff_thread = THREAD_NULL;
                handoff_option = THREAD_HANDOFF_SETRUN_NEEDED;
        }
        /*
         * Now, we can block.  If the caller supplied a continuation
         * pointer of his own for after the block, block with the
         * appropriate semaphore continuation.  This will gather the
         * semaphore results, release references on the semaphore(s),
         * and then call the caller's continuation.
         */
        if (caller_cont) {
                self->sth_continuation = caller_cont;
                self->sth_waitsemaphore = wait_semaphore;
                self->sth_signalsemaphore = signal_semaphore;

                thread_handoff_parameter(handoff_thread, semaphore_wait_continue,
                    NULL, handoff_option);
        } else {
                wait_result = thread_handoff_deallocate(handoff_thread, handoff_option);
        }

        assert(self->handoff_thread == THREAD_NULL);
        return semaphore_convert_wait_result(wait_result);
}


/*
 *      Routine:        semaphore_wait
 *
 *      Traditional (non-continuation) interface presented to
 *      in-kernel clients to wait on a semaphore.
 */
kern_return_t
semaphore_wait(
        semaphore_t             semaphore)
{
        if (semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        return semaphore_wait_internal(semaphore,
                   SEMAPHORE_NULL,
                   0ULL, SEMAPHORE_OPTION_NONE,
                   (void (*)(kern_return_t))0);
}

kern_return_t
semaphore_wait_noblock(
        semaphore_t             semaphore)
{
        if (semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        return semaphore_wait_internal(semaphore,
                   SEMAPHORE_NULL,
                   0ULL, SEMAPHORE_TIMEOUT_NOBLOCK,
                   (void (*)(kern_return_t))0);
}

kern_return_t
semaphore_wait_deadline(
        semaphore_t             semaphore,
        uint64_t                deadline)
{
        if (semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        return semaphore_wait_internal(semaphore,
                   SEMAPHORE_NULL,
                   deadline, SEMAPHORE_OPTION_NONE,
                   (void (*)(kern_return_t))0);
}

/*
 *      Trap:   semaphore_wait_trap
 *
 *      Trap version of semaphore wait.  Called on behalf of user-level
 *      clients.
 */

kern_return_t
semaphore_wait_trap(
        struct semaphore_wait_trap_args *args)
{
        return semaphore_wait_trap_internal(args->wait_name, thread_syscall_return);
}



kern_return_t
semaphore_wait_trap_internal(
        mach_port_name_t name,
        void (*caller_cont)(kern_return_t))
{
        semaphore_t     semaphore;
        kern_return_t kr;

        kr = port_name_to_semaphore(name, &semaphore);
        if (kr == KERN_SUCCESS) {
                kr = semaphore_wait_internal(semaphore,
                    SEMAPHORE_NULL,
                    0ULL, SEMAPHORE_OPTION_NONE,
                    caller_cont);
                semaphore_dereference(semaphore);
        }
        return kr;
}

/*
 *      Routine:        semaphore_timedwait
 *
 *      Traditional (non-continuation) interface presented to
 *      in-kernel clients to wait on a semaphore with a timeout.
 *
 *      A timeout of {0,0} is considered non-blocking.
 */
kern_return_t
semaphore_timedwait(
        semaphore_t             semaphore,
        mach_timespec_t         wait_time)
{
        int                             option = SEMAPHORE_OPTION_NONE;
        uint64_t                deadline = 0;

        if (semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        if (BAD_MACH_TIMESPEC(&wait_time)) {
                return KERN_INVALID_VALUE;
        }

        if (wait_time.tv_sec == 0 && wait_time.tv_nsec == 0) {
                option = SEMAPHORE_TIMEOUT_NOBLOCK;
        } else {
                deadline = semaphore_deadline(wait_time.tv_sec, wait_time.tv_nsec);
        }

        return semaphore_wait_internal(semaphore,
                   SEMAPHORE_NULL,
                   deadline, option,
                   (void (*)(kern_return_t))0);
}

/*
 *      Trap:   semaphore_timedwait_trap
 *
 *      Trap version of a semaphore_timedwait.  The timeout parameter
 *      is passed in two distinct parts and re-assembled on this side
 *      of the trap interface (to accomodate calling conventions that
 *      pass structures as pointers instead of inline in registers without
 *      having to add a copyin).
 *
 *      A timeout of {0,0} is considered non-blocking.
 */
kern_return_t
semaphore_timedwait_trap(
        struct semaphore_timedwait_trap_args *args)
{
        return semaphore_timedwait_trap_internal(args->wait_name, args->sec, args->nsec, thread_syscall_return);
}


kern_return_t
semaphore_timedwait_trap_internal(
        mach_port_name_t name,
        unsigned int            sec,
        clock_res_t             nsec,
        void (*caller_cont)(kern_return_t))
{
        semaphore_t semaphore;
        mach_timespec_t wait_time;
        kern_return_t kr;

        wait_time.tv_sec = sec;
        wait_time.tv_nsec = nsec;
        if (BAD_MACH_TIMESPEC(&wait_time)) {
                return KERN_INVALID_VALUE;
        }

        kr = port_name_to_semaphore(name, &semaphore);
        if (kr == KERN_SUCCESS) {
                int                             option = SEMAPHORE_OPTION_NONE;
                uint64_t                deadline = 0;

                if (sec == 0 && nsec == 0) {
                        option = SEMAPHORE_TIMEOUT_NOBLOCK;
                } else {
                        deadline = semaphore_deadline(sec, nsec);
                }

                kr = semaphore_wait_internal(semaphore,
                    SEMAPHORE_NULL,
                    deadline, option,
                    caller_cont);
                semaphore_dereference(semaphore);
        }
        return kr;
}

/*
 *      Routine:        semaphore_wait_signal
 *
 *      Atomically register a wait on a semaphore and THEN signal
 *      another.  This is the in-kernel entry point that does not
 *      block at a continuation and does not free a signal_semaphore
 *      reference.
 */
kern_return_t
semaphore_wait_signal(
        semaphore_t             wait_semaphore,
        semaphore_t             signal_semaphore)
{
        if (wait_semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        return semaphore_wait_internal(wait_semaphore,
                   signal_semaphore,
                   0ULL, SEMAPHORE_OPTION_NONE,
                   (void (*)(kern_return_t))0);
}

/*
 *      Trap:   semaphore_wait_signal_trap
 *
 *      Atomically register a wait on a semaphore and THEN signal
 *      another.  This is the trap version from user space.
 */
kern_return_t
semaphore_wait_signal_trap(
        struct semaphore_wait_signal_trap_args *args)
{
        return semaphore_wait_signal_trap_internal(args->wait_name, args->signal_name, thread_syscall_return);
}

kern_return_t
semaphore_wait_signal_trap_internal(
        mach_port_name_t wait_name,
        mach_port_name_t signal_name,
        void (*caller_cont)(kern_return_t))
{
        semaphore_t wait_semaphore;
        semaphore_t signal_semaphore;
        kern_return_t kr;

        kr = port_name_to_semaphore(signal_name, &signal_semaphore);
        if (kr == KERN_SUCCESS) {
                kr = port_name_to_semaphore(wait_name, &wait_semaphore);
                if (kr == KERN_SUCCESS) {
                        kr = semaphore_wait_internal(wait_semaphore,
                            signal_semaphore,
                            0ULL, SEMAPHORE_OPTION_NONE,
                            caller_cont);
                        semaphore_dereference(wait_semaphore);
                }
                semaphore_dereference(signal_semaphore);
        }
        return kr;
}


/*
 *      Routine:        semaphore_timedwait_signal
 *
 *      Atomically register a wait on a semaphore and THEN signal
 *      another.  This is the in-kernel entry point that does not
 *      block at a continuation.
 *
 *      A timeout of {0,0} is considered non-blocking.
 */
kern_return_t
semaphore_timedwait_signal(
        semaphore_t             wait_semaphore,
        semaphore_t             signal_semaphore,
        mach_timespec_t         wait_time)
{
        int                             option = SEMAPHORE_OPTION_NONE;
        uint64_t                deadline = 0;

        if (wait_semaphore == SEMAPHORE_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        if (BAD_MACH_TIMESPEC(&wait_time)) {
                return KERN_INVALID_VALUE;
        }

        if (wait_time.tv_sec == 0 && wait_time.tv_nsec == 0) {
                option = SEMAPHORE_TIMEOUT_NOBLOCK;
        } else {
                deadline = semaphore_deadline(wait_time.tv_sec, wait_time.tv_nsec);
        }

        return semaphore_wait_internal(wait_semaphore,
                   signal_semaphore,
                   deadline, option,
                   (void (*)(kern_return_t))0);
}

/*
 *      Trap:   semaphore_timedwait_signal_trap
 *
 *      Atomically register a timed wait on a semaphore and THEN signal
 *      another.  This is the trap version from user space.
 */
kern_return_t
semaphore_timedwait_signal_trap(
        struct semaphore_timedwait_signal_trap_args *args)
{
        return semaphore_timedwait_signal_trap_internal(args->wait_name, args->signal_name, args->sec, args->nsec, thread_syscall_return);
}

kern_return_t
semaphore_timedwait_signal_trap_internal(
        mach_port_name_t wait_name,
        mach_port_name_t signal_name,
        unsigned int sec,
        clock_res_t nsec,
        void (*caller_cont)(kern_return_t))
{
        semaphore_t wait_semaphore;
        semaphore_t signal_semaphore;
        mach_timespec_t wait_time;
        kern_return_t kr;

        wait_time.tv_sec = sec;
        wait_time.tv_nsec = nsec;
        if (BAD_MACH_TIMESPEC(&wait_time)) {
                return KERN_INVALID_VALUE;
        }

        kr = port_name_to_semaphore(signal_name, &signal_semaphore);
        if (kr == KERN_SUCCESS) {
                kr = port_name_to_semaphore(wait_name, &wait_semaphore);
                if (kr == KERN_SUCCESS) {
                        int                             option = SEMAPHORE_OPTION_NONE;
                        uint64_t                deadline = 0;

                        if (sec == 0 && nsec == 0) {
                                option = SEMAPHORE_TIMEOUT_NOBLOCK;
                        } else {
                                deadline = semaphore_deadline(sec, nsec);
                        }

                        kr = semaphore_wait_internal(wait_semaphore,
                            signal_semaphore,
                            deadline, option,
                            caller_cont);
                        semaphore_dereference(wait_semaphore);
                }
                semaphore_dereference(signal_semaphore);
        }
        return kr;
}


/*
 *      Routine:        semaphore_reference
 *
 *      Take out a reference on a semaphore.  This keeps the data structure
 *      in existence (but the semaphore may be deactivated).
 */
void
semaphore_reference(
        semaphore_t             semaphore)
{
        os_ref_retain(&semaphore->ref_count);
}

/*
 *      Routine:        semaphore_dereference
 *
 *      Release a reference on a semaphore.  If this is the last reference,
 *      the semaphore data structure is deallocated.
 */
void
semaphore_dereference(
        semaphore_t             semaphore)
{
        uint32_t collisions;
        spl_t spl_level;

        if (semaphore == NULL) {
                return;
        }

        if (os_ref_release(&semaphore->ref_count) > 0) {
                return;
        }

        /*
         * Last ref, clean up the port [if any]
         * associated with the semaphore, destroy
         * it (if still active) and then free
         * the semaphore.
         */
        ipc_port_t port = semaphore->port;

        if (IP_VALID(port)) {
                assert(!port->ip_srights);
                ipc_port_dealloc_kernel(port);
        }

        /*
         * Lock the semaphore to lock in the owner task reference.
         * Then continue to try to lock the task (inverse order).
         */
        spl_level = splsched();
        semaphore_lock(semaphore);
        for (collisions = 0; semaphore->active; collisions++) {
                task_t task = semaphore->owner;

                assert(task != TASK_NULL);

                if (task_lock_try(task)) {
                        semaphore_destroy_internal(task, semaphore);
                        /* semaphore unlocked */
                        splx(spl_level);
                        task_unlock(task);
                        goto out;
                }

                /* failed to get out-of-order locks */
                semaphore_unlock(semaphore);
                splx(spl_level);
                mutex_pause(collisions);
                spl_level = splsched();
                semaphore_lock(semaphore);
        }
        semaphore_unlock(semaphore);
        splx(spl_level);

out:
        zfree(semaphore_zone, semaphore);
}

#define WAITQ_TO_SEMA(wq) ((semaphore_t) ((uintptr_t)(wq) - offsetof(struct semaphore, waitq)))
void
kdp_sema_find_owner(struct waitq * waitq, __assert_only event64_t event, thread_waitinfo_t * waitinfo)
{
        semaphore_t sem = WAITQ_TO_SEMA(waitq);
        assert(event == SEMAPHORE_EVENT);

        zone_require(semaphore_zone, sem);

        waitinfo->context = VM_KERNEL_UNSLIDE_OR_PERM(sem->port);
        if (sem->owner) {
                waitinfo->owner = pid_from_task(sem->owner);
        }
}