Add an implementation of a generic sleep queue abstraction that is used

to queue threads sleeping on a wait channel similar to how turnstiles are
used to queue threads waiting for a lock.  This subsystem will be used as
the backend for sleep/wakeup and condition variables initially.  Eventually
it will also be used to replace the ithread-specific iwait thread
inhibitor.

Sleep queues are also not locked by sched_lock, so this splits sched_lock
up a bit further increasing concurrency within the scheduler.  Sleep queues
also natively support timeouts on sleeps and interruptible sleeps allowing
for the reduction of a lot of duplicated code between the sleep/wakeup and
condition variable implementations.  For more details on the sleep queue
implementation, check the comments in sys/sleepqueue.h and
kern/subr_sleepqueue.c.

1 files changed, 776 insertions, 0 deletions

diff --git a/sys/kern/subr_sleepqueue.c b/sys/kern/subr_sleepqueue.c
new file mode 100644
index 0000000..9b406ee
--- /dev/null
+++ b/sys/kern/subr_sleepqueue.c
@@ -0,0 +1,776 @@
+/*
+ * Copyright (c) 2004 John Baldwin <jhb@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the author nor the names of any co-contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * Implementation of sleep queues used to hold queue of threads blocked on
+ * a wait channel.  Sleep queues different from turnstiles in that wait
+ * channels are not owned by anyone, so there is no priority propagation.
+ * Sleep queues can also provide a timeout and can also be interrupted by
+ * signals.  That said, there are several similarities between the turnstile
+ * and sleep queue implementations.  (Note: turnstiles were implemented
+ * first.)  For example, both use a hash table of the same size where each
+ * bucket is referred to as a "chain" that contains both a spin lock and
+ * a linked list of queues.  An individual queue is located by using a hash
+ * to pick a chain, locking the chain, and then walking the chain searching
+ * for the queue.  This means that a wait channel object does not need to
+ * embed it's queue head just as locks do not embed their turnstile queue
+ * head.  Threads also carry around a sleep queue that they lend to the
+ * wait channel when blocking.  Just as in turnstiles, the queue includes
+ * a free list of the sleep queues of other threads blocked on the same
+ * wait channel in the case of multiple waiters.
+ *
+ * Some additional functionality provided by sleep queues include the
+ * ability to set a timeout.  The timeout is managed using a per-thread
+ * callout that resumes a thread if it is asleep.  A thread may also
+ * catch signals while it is asleep (aka an interruptible sleep).  The
+ * signal code uses sleepq_abort() to interrupt a sleeping thread.  Finally,
+ * sleep queues also provide some extra assertions.  One is not allowed to
+ * mix the sleep/wakeup and cv APIs for a given wait channel.  Also, one
+ * must consistently use the same lock to synchronize with a wait channel,
+ * though this check is currently only a warning for sleep/wakeup due to
+ * pre-existing abuse of that API.  The same lock must also be held when
+ * awakening threads, though that is currently only enforced for condition
+ * variables.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/lock.h>
+#include <sys/kernel.h>
+#include <sys/ktr.h>
+#include <sys/malloc.h>
+#include <sys/mutex.h>
+#include <sys/proc.h>
+#include <sys/sched.h>
+#include <sys/signalvar.h>
+#include <sys/sleepqueue.h>
+
+/*
+ * Constants for the hash table of sleep queue chains.  These constants are
+ * the same ones that 4BSD (and possibly earlier versions of BSD) used.
+ * Basically, we ignore the lower 8 bits of the address since most wait
+ * channel pointers are aligned and only look at the next 7 bits for the
+ * hash.  SC_TABLESIZE must be a power of two for SC_MASK to work properly.
+ */
+#define	SC_TABLESIZE	128			/* Must be power of 2. */
+#define	SC_MASK		(SC_TABLESIZE - 1)
+#define	SC_SHIFT	8
+#define	SC_HASH(wc)	(((uintptr_t)(wc) >> SC_SHIFT) & SC_MASK)
+#define	SC_LOOKUP(wc)	&sleepq_chains[SC_HASH(wc)]
+
+/*
+ * There two different lists of sleep queues.  Both lists are connected
+ * via the sq_hash entries.  The first list is the sleep queue chain list
+ * that a sleep queue is on when it is attached to a wait channel.  The
+ * second list is the free list hung off of a sleep queue that is attached
+ * to a wait channel.
+ *
+ * Each sleep queue also contains the wait channel it is attached to, the
+ * list of threads blocked on that wait channel, flags specific to the
+ * wait channel, and the lock used to synchronize with a wait channel.
+ * The flags are used to catch mismatches between the various consumers
+ * of the sleep queue API (e.g. sleep/wakeup and condition variables).
+ * The lock pointer is only used when invariants are enabled for various
+ * debugging checks.
+ *
+ * Locking key:
+ *  c - sleep queue chain lock
+ */
+struct sleepqueue {
+	TAILQ_HEAD(, thread) sq_blocked;	/* (c) Blocked threads. */
+	LIST_ENTRY(sleepqueue) sq_hash;		/* (c) Chain and free list. */
+	LIST_HEAD(, sleepqueue) sq_free;	/* (c) Free queues. */
+	void	*sq_wchan;			/* (c) Wait channel. */
+	int	sq_flags;			/* (c) Flags. */
+#ifdef INVARIANTS
+	struct mtx *sq_lock;			/* (c) Associated lock. */
+#endif
+};
+
+struct sleepqueue_chain {
+	LIST_HEAD(, sleepqueue) sc_queues;	/* List of sleep queues. */
+	struct mtx sc_lock;			/* Spin lock for this chain. */
+};
+
+static struct sleepqueue_chain sleepq_chains[SC_TABLESIZE];
+
+MALLOC_DEFINE(M_SLEEPQUEUE, "sleep queues", "sleep queues");
+
+/*
+ * Prototypes for non-exported routines.
+ */
+static int	sleepq_check_timeout(void);
+static void	sleepq_switch(void *wchan);
+static void	sleepq_timeout(void *arg);
+static void	sleepq_wakeup_thread(struct sleepqueue *sq, struct thread *td,
+		    int pri);
+
+/*
+ * Early initialization of sleep queues that is called from the sleepinit()
+ * SYSINIT.
+ */
+void
+init_sleepqueues(void)
+{
+	int i;
+
+	for (i = 0; i < SC_TABLESIZE; i++) {
+		LIST_INIT(&sleepq_chains[i].sc_queues);
+		mtx_init(&sleepq_chains[i].sc_lock, "sleepq chain", NULL,
+		    MTX_SPIN);
+	}
+	thread0.td_sleepqueue = sleepq_alloc();
+}
+
+/*
+ * Malloc and initialize a new sleep queue for a new thread.
+ */
+struct sleepqueue *
+sleepq_alloc(void)
+{
+	struct sleepqueue *sq;
+
+	sq = malloc(sizeof(struct sleepqueue), M_SLEEPQUEUE, M_WAITOK | M_ZERO);
+	TAILQ_INIT(&sq->sq_blocked);
+	LIST_INIT(&sq->sq_free);
+	return (sq);
+}
+
+/*
+ * Free a sleep queue when a thread is destroyed.
+ */
+void
+sleepq_free(struct sleepqueue *sq)
+{
+
+	MPASS(sq != NULL);
+	MPASS(TAILQ_EMPTY(&sq->sq_blocked));
+	free(sq, M_SLEEPQUEUE);
+}
+
+/*
+ * Look up the sleep queue associated with a given wait channel in the hash
+ * table locking the associated sleep queue chain.  Return holdind the sleep
+ * queue chain lock.  If no queue is found in the table, NULL is returned.
+ */
+struct sleepqueue *
+sleepq_lookup(void *wchan)
+{
+	struct sleepqueue_chain *sc;
+	struct sleepqueue *sq;
+
+	KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
+	sc = SC_LOOKUP(wchan);
+	mtx_lock_spin(&sc->sc_lock);
+	LIST_FOREACH(sq, &sc->sc_queues, sq_hash)
+		if (sq->sq_wchan == wchan)
+			return (sq);
+	return (NULL);
+}
+
+/*
+ * Unlock the sleep queue chain associated with a given wait channel.
+ */
+void
+sleepq_release(void *wchan)
+{
+	struct sleepqueue_chain *sc;
+
+	sc = SC_LOOKUP(wchan);
+	mtx_unlock_spin(&sc->sc_lock);
+}
+
+/*
+ * Places the current thread on the sleepqueue for the specified wait
+ * channel.  If INVARIANTS is enabled, then it associates the passed in
+ * lock with the sleepq to make sure it is held when that sleep queue is
+ * woken up.
+ */
+void
+sleepq_add(struct sleepqueue *sq, void *wchan, struct mtx *lock,
+    const char *wmesg, int flags)
+{
+	struct sleepqueue_chain *sc;
+	struct thread *td, *td1;
+
+	td = curthread;
+	sc = SC_LOOKUP(wchan);
+	mtx_assert(&sc->sc_lock, MA_OWNED);
+	MPASS(td->td_sleepqueue != NULL);
+	MPASS(wchan != NULL);
+
+	/* If the passed in sleep queue is NULL, use this thread's queue. */
+	if (sq == NULL) {
+		sq = td->td_sleepqueue;
+		LIST_INSERT_HEAD(&sc->sc_queues, sq, sq_hash);
+		KASSERT(TAILQ_EMPTY(&sq->sq_blocked),
+		    ("thread's sleep queue has a non-empty queue"));
+		KASSERT(LIST_EMPTY(&sq->sq_free),
+		    ("thread's sleep queue has a non-empty free list"));
+		KASSERT(sq->sq_wchan == NULL, ("stale sq_wchan pointer"));
+		sq->sq_wchan = wchan;
+#ifdef INVARIANTS
+		sq->sq_lock = lock;
+#endif
+		sq->sq_flags = flags;
+		TAILQ_INSERT_TAIL(&sq->sq_blocked, td, td_slpq);
+	} else {
+		MPASS(wchan == sq->sq_wchan);
+#ifdef INVARIANTS
+		if (flags & SLEEPQ_CONDVAR)
+			MPASS(lock == sq->sq_lock);
+		else if (lock != sq->sq_lock) {
+			/*
+			 * When msleep() abusers are fixed this should
+			 * change back to the simple MPASS() for all
+			 * sleep queues.
+			 */
+			printf("Mismatched locks to msleep(%p, %s):\n",
+			    wchan, wmesg);
+			printf("  old %p (%s), new %p (%s)\n", sq->sq_lock,
+			    sq->sq_lock == NULL ? "null" :
+			    sq->sq_lock->mtx_object.lo_name, lock,
+			    lock == NULL ? "null" :
+			    lock->mtx_object.lo_name);
+			backtrace();
+		}
+#endif
+		TAILQ_FOREACH(td1, &sq->sq_blocked, td_slpq)
+			if (td1->td_priority > td->td_priority)
+				break;
+		if (td1 != NULL)
+			TAILQ_INSERT_BEFORE(td1, td, td_slpq);
+		else
+			TAILQ_INSERT_TAIL(&sq->sq_blocked, td, td_slpq);
+		LIST_INSERT_HEAD(&sq->sq_free, td->td_sleepqueue, sq_hash);
+	}
+	td->td_sleepqueue = NULL;
+	mtx_lock_spin(&sched_lock);
+	td->td_wchan = wchan;
+	td->td_wmesg = wmesg;
+	mtx_unlock_spin(&sched_lock);
+}
+
+/*
+ * Sets a timeout that will remove the current thread from the specified
+ * sleep queue after timo ticks if the thread has not already been awakened.
+ */
+void
+sleepq_set_timeout(struct sleepqueue *sq, void *wchan, int timo)
+{
+	struct sleepqueue_chain *sc;
+	struct thread *td;
+
+	td = curthread;
+	sc = SC_LOOKUP(wchan);
+	mtx_assert(&sc->sc_lock, MA_OWNED);
+	MPASS(TD_ON_SLEEPQ(td));
+	MPASS(td->td_sleepqueue == NULL);
+	MPASS(wchan != NULL);
+	callout_reset(&td->td_slpcallout, timo, sleepq_timeout, td);
+}
+
+/*
+ * Marks the pending sleep of the current thread as interruptible and
+ * makes an initial check for pending signals before putting a thread
+ * to sleep.
+ */
+int
+sleepq_catch_signals(void *wchan)
+{
+	struct sleepqueue_chain *sc;
+	struct sleepqueue *sq;
+	struct thread *td;
+	struct proc *p;
+	int sig;
+
+	td = curthread;
+	p = td->td_proc;
+	sc = SC_LOOKUP(wchan);
+	mtx_assert(&sc->sc_lock, MA_OWNED);
+	MPASS(td->td_sleepqueue == NULL);
+	MPASS(wchan != NULL);
+	CTR3(KTR_PROC, "sleepq catching signals: thread %p (pid %d, %s)", td,
+	    p->p_pid, p->p_comm);
+
+	/* Mark thread as being in an interruptible sleep. */
+	mtx_lock_spin(&sched_lock);
+	MPASS(TD_ON_SLEEPQ(td));
+	td->td_flags |= TDF_SINTR;
+	mtx_unlock_spin(&sched_lock);
+	sleepq_release(wchan);
+
+	/* See if there are any pending signals for this thread. */
+	PROC_LOCK(p);
+	mtx_lock(&p->p_sigacts->ps_mtx);
+	sig = cursig(td);
+	mtx_unlock(&p->p_sigacts->ps_mtx);
+	if (sig == 0 && thread_suspend_check(1))
+		sig = SIGSTOP;
+	PROC_UNLOCK(p);
+
+	/*
+	 * If there were pending signals and this thread is still on
+	 * the sleep queue, remove it from the sleep queue.
+	 */
+	sq = sleepq_lookup(wchan);
+	mtx_lock_spin(&sched_lock);
+	if (TD_ON_SLEEPQ(td) && sig != 0) {
+		mtx_unlock_spin(&sched_lock);
+		sleepq_wakeup_thread(sq, td, -1);
+	} else
+		mtx_unlock_spin(&sched_lock);
+	return (sig);
+}
+
+/*
+ * Switches to another thread if we are still asleep on a sleep queue and
+ * drop the lock on the sleepqueue chain.  Returns with sched_lock held.
+ */
+static void
+sleepq_switch(void *wchan)
+{
+	struct sleepqueue_chain *sc;
+	struct thread *td;
+
+	td = curthread;
+	sc = SC_LOOKUP(wchan);
+	mtx_assert(&sc->sc_lock, MA_OWNED);
+
+	/* 
+	 * If we have a sleep queue, then we've already been woken up, so
+	 * just return.
+	 */
+	if (td->td_sleepqueue != NULL) {
+		MPASS(!TD_ON_SLEEPQ(td));
+		mtx_unlock_spin(&sc->sc_lock);
+		mtx_lock_spin(&sched_lock);
+		return;
+	}
+
+	/*
+	 * Otherwise, actually go to sleep.
+	 */
+	mtx_lock_spin(&sched_lock);
+	mtx_unlock_spin(&sc->sc_lock);
+
+	sched_sleep(td);
+	TD_SET_SLEEPING(td);
+	mi_switch(SW_VOL);
+	KASSERT(TD_IS_RUNNING(td), ("running but not TDS_RUNNING"));
+	CTR3(KTR_PROC, "sleepq resume: thread %p (pid %d, %s)", td,
+	    td->td_proc->p_pid, td->td_proc->p_comm);
+}
+
+/*
+ * Check to see if we timed out.
+ */
+static int
+sleepq_check_timeout(void)
+{
+	struct thread *td;
+
+	mtx_assert(&sched_lock, MA_OWNED);
+	td = curthread;
+
+	/*
+	 * If TDF_TIMEOUT is set, we timed out.
+	 */
+	if (td->td_flags & TDF_TIMEOUT) {
+		td->td_flags &= ~TDF_TIMEOUT;
+		return (EWOULDBLOCK);
+	}
+
+	/*
+	 * If TDF_TIMOFAIL is set, the timeout ran after we had
+	 * already been woken up.
+	 */
+	if (td->td_flags & TDF_TIMOFAIL)
+		td->td_flags &= ~TDF_TIMOFAIL;
+
+	/*
+	 * If callout_stop() fails, then the timeout is running on
+	 * another CPU, so synchronize with it to avoid having it
+	 * accidentally wake up a subsequent sleep.
+	 */
+	else if (callout_stop(&td->td_slpcallout) == 0) {
+		td->td_flags |= TDF_TIMEOUT;
+		TD_SET_SLEEPING(td);
+		mi_switch(SW_INVOL);
+	}
+	return (0);
+}
+
+/*
+ * Check to see if we were awoken by a signal.
+ */
+static int
+sleepq_check_signals(void)
+{
+	struct thread *td;
+
+	mtx_assert(&sched_lock, MA_OWNED);
+	td = curthread;
+
+	/* We are no longer in an interruptible sleep. */
+	td->td_flags &= ~TDF_SINTR;
+
+	/* If we were interrupted, return td_intrval. */
+	if (td->td_flags & TDF_INTERRUPT)
+		return (td->td_intrval);
+	return (0);
+}
+
+/*
+ * If we were in an interruptible sleep and we weren't interrupted and
+ * didn't timeout, check to see if there are any pending signals and
+ * which return value we should use if so.  The return value from an
+ * earlier call to sleepq_catch_signals() should be passed in as the
+ * argument.
+ */
+int
+sleepq_calc_signal_retval(int sig)
+{
+	struct thread *td;
+	struct proc *p;
+	int rval;
+
+	td = curthread;
+	p = td->td_proc;
+	PROC_LOCK(p);
+	mtx_lock(&p->p_sigacts->ps_mtx);
+	/* XXX: Should we always be calling cursig()? */
+	if (sig == 0)
+		sig = cursig(td);
+	if (sig != 0) {
+		if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
+			rval = EINTR;
+		else
+			rval = ERESTART;
+	} else
+		rval = 0;
+	mtx_unlock(&p->p_sigacts->ps_mtx);
+	PROC_UNLOCK(p);
+	return (rval);
+}
+
+/*
+ * Block the current thread until it is awakened from its sleep queue.
+ */
+void
+sleepq_wait(void *wchan)
+{
+
+	sleepq_switch(wchan);
+	mtx_unlock_spin(&sched_lock);
+}
+
+/*
+ * Block the current thread until it is awakened from its sleep queue
+ * or it is interrupted by a signal.
+ */
+int
+sleepq_wait_sig(void *wchan)
+{
+	int rval;
+
+	sleepq_switch(wchan);
+	rval = sleepq_check_signals();
+	mtx_unlock_spin(&sched_lock); 
+	return (rval);
+}
+
+/*
+ * Block the current thread until it is awakened from its sleep queue
+ * or it times out while waiting.
+ */
+int
+sleepq_timedwait(void *wchan, int signal_caught)
+{
+	int rval;
+
+	sleepq_switch(wchan);
+	rval = sleepq_check_timeout();
+	mtx_unlock_spin(&sched_lock);
+	if (signal_caught)
+		return (0);
+	else
+		return (rval);
+}
+
+/*
+ * Block the current thread until it is awakened from its sleep queue,
+ * it is interrupted by a signal, or it times out waiting to be awakened.
+ */
+int
+sleepq_timedwait_sig(void *wchan, int signal_caught)
+{
+	int rvalt, rvals;
+
+	sleepq_switch(wchan);
+	rvalt = sleepq_check_timeout();
+	rvals = sleepq_check_signals();
+	mtx_unlock_spin(&sched_lock);
+	if (signal_caught || rvalt == 0)
+		return (rvals);
+	else
+		return (rvalt);
+}
+
+/*
+ * Removes a thread from a sleep queue and resumes it.
+ */
+static void
+sleepq_wakeup_thread(struct sleepqueue *sq, struct thread *td, int pri)
+{
+	struct sleepqueue_chain *sc;
+
+	MPASS(td != NULL);
+	MPASS(sq->sq_wchan != NULL);
+	MPASS(td->td_wchan == sq->sq_wchan);
+	sc = SC_LOOKUP(sq->sq_wchan);
+	mtx_assert(&sc->sc_lock, MA_OWNED);
+
+	/* Remove the thread from the queue. */
+	TAILQ_REMOVE(&sq->sq_blocked, td, td_slpq);
+
+	/*
+	 * Get a sleep queue for this thread.  If this is the last waiter,
+	 * use the queue itself and take it out of the chain, otherwise,
+	 * remove a queue from the free list.
+	 */
+	if (LIST_EMPTY(&sq->sq_free)) {
+		td->td_sleepqueue = sq;
+#ifdef INVARIANTS
+		sq->sq_wchan = NULL;
+#endif
+	} else
+		td->td_sleepqueue = LIST_FIRST(&sq->sq_free);
+	LIST_REMOVE(td->td_sleepqueue, sq_hash);
+
+	/*
+	 * Finish resuming the thread.
+	 */
+	mtx_lock_spin(&sched_lock);
+	CTR3(KTR_PROC, "sleepq_wakeup: thread %p (pid %d, %s)", td,
+	    td->td_proc->p_pid, td->td_proc->p_comm);
+	td->td_wmesg = NULL;
+	td->td_wchan = NULL;
+	TD_CLR_SLEEPING(td);
+
+	/* Adjust priority if requested. */
+	MPASS(pri == -1 || (pri >= PRI_MIN && pri <= PRI_MAX));
+	if (pri != -1 && td->td_priority > pri)
+		td->td_priority = pri;
+	setrunnable(td);
+	mtx_unlock_spin(&sched_lock);
+}
+
+/*
+ * Find the highest priority thread sleeping on a wait channel and resume it.
+ */
+void
+sleepq_signal(void *wchan, int flags, int pri)
+{
+	struct sleepqueue *sq;
+
+	CTR2(KTR_PROC, "sleepq_signal(%p, %d)", wchan, flags);
+	KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
+	sq = sleepq_lookup(wchan);
+	if (sq == NULL) {
+		sleepq_release(wchan);
+		return;
+	}
+	KASSERT(sq->sq_flags == flags,
+	    ("%s: mismatch between sleep/wakeup and cv_*", __func__));
+	/* XXX: Do for all sleep queues eventually. */
+	if (flags & SLEEPQ_CONDVAR)
+		mtx_assert(sq->sq_lock, MA_OWNED);
+	sleepq_wakeup_thread(sq, TAILQ_FIRST(&sq->sq_blocked), pri);
+	sleepq_release(wchan);
+}
+
+/*
+ * Resume all threads sleeping on a specified wait channel.
+ */
+void
+sleepq_broadcast(void *wchan, int flags, int pri)
+{
+	struct sleepqueue *sq;
+
+	CTR2(KTR_PROC, "sleepq_broadcast(%p, %d)", wchan, flags);
+	KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
+	sq = sleepq_lookup(wchan);
+	if (sq == NULL) {
+		sleepq_release(wchan);
+		return;
+	}
+	KASSERT(sq->sq_flags == flags,
+	    ("%s: mismatch between sleep/wakeup and cv_*", __func__));
+	/* XXX: Do for all sleep queues eventually. */
+	if (flags & SLEEPQ_CONDVAR)
+		mtx_assert(sq->sq_lock, MA_OWNED);
+	while (!TAILQ_EMPTY(&sq->sq_blocked))
+		sleepq_wakeup_thread(sq, TAILQ_FIRST(&sq->sq_blocked), pri);
+	sleepq_release(wchan);
+}
+
+/*
+ * Time sleeping threads out.  When the timeout expires, the thread is
+ * removed from the sleep queue and made runnable if it is still asleep.
+ */
+static void
+sleepq_timeout(void *arg)
+{
+	struct sleepqueue *sq;
+	struct thread *td;
+	void *wchan;
+
+	td = (struct thread *)arg;
+	CTR3(KTR_PROC, "sleepq_timeout: thread %p (pid %d, %s)",
+	    td, td->td_proc->p_pid, td->td_proc->p_comm);
+
+	/*
+	 * First, see if the thread is asleep and get the wait channel if
+	 * it is.
+	 */
+	mtx_lock_spin(&sched_lock);
+	if (TD_ON_SLEEPQ(td)) {
+		wchan = td->td_wchan;
+		mtx_unlock_spin(&sched_lock);
+		sq = sleepq_lookup(wchan);
+		mtx_lock_spin(&sched_lock);
+	} else {
+		wchan = NULL;
+		sq = NULL;
+	}
+
+	/*
+	 * At this point, if the thread is still on the sleep queue,
+	 * we have that sleep queue locked as it cannot migrate sleep
+	 * queues while we dropped sched_lock.  If it had resumed and
+	 * was on another CPU while the lock was dropped, it would have
+	 * seen that TDF_TIMEOUT and TDF_TIMOFAIL are clear and the
+	 * call to callout_stop() to stop this routine would have failed
+	 * meaning that it would have already set TDF_TIMEOUT to
+	 * synchronize with this function.
+	 */
+	if (TD_ON_SLEEPQ(td)) {
+		MPASS(TD_IS_SLEEPING(td));
+		MPASS(td->td_wchan == wchan);
+		MPASS(sq != NULL);
+		td->td_flags |= TDF_TIMEOUT;
+		mtx_unlock_spin(&sched_lock);
+		sleepq_wakeup_thread(sq, td, -1);
+		sleepq_release(wchan);
+		return;
+	} else if (wchan != NULL)
+		sleepq_release(wchan);
+
+	/*
+	 * Now check for the edge cases.  First, if TDF_TIMEOUT is set,
+	 * then the other thread has already yielded to us, so clear
+	 * the flag and resume it.  If TDF_TIMEOUT is not set, then the
+	 * we know that the other thread is not on a sleep queue, but it
+	 * hasn't resumed execution yet.  In that case, set TDF_TIMOFAIL
+	 * to let it know that the timeout has already run and doesn't
+	 * need to be canceled.
+	 */
+	if (td->td_flags & TDF_TIMEOUT) {
+		td->td_flags &= ~TDF_TIMEOUT;
+		TD_CLR_SLEEPING(td);
+		setrunnable(td);
+	} else
+		td->td_flags |= TDF_TIMOFAIL;
+	mtx_unlock_spin(&sched_lock);
+}
+
+/*
+ * Resumes a specific thread from the sleep queue associated with a specific
+ * wait channel if it is on that queue.
+ */
+void
+sleepq_remove(struct thread *td, void *wchan)
+{
+	struct sleepqueue *sq;
+
+	/*
+	 * Look up the sleep queue for this wait channel, then re-check
+	 * that the thread is asleep on that channel, if it is not, then
+	 * bail.
+	 */
+	MPASS(wchan != NULL);
+	sq = sleepq_lookup(wchan);
+	mtx_lock_spin(&sched_lock);
+	if (!TD_ON_SLEEPQ(td) || td->td_wchan != wchan) {
+		mtx_unlock_spin(&sched_lock);
+		sleepq_release(wchan);
+		return;
+	}
+	mtx_unlock_spin(&sched_lock);
+	MPASS(sq != NULL);
+
+	/* Thread is asleep on sleep queue sq, so wake it up. */
+	sleepq_wakeup_thread(sq, td, -1);
+	sleepq_release(wchan);
+}
+
+/*
+ * Abort a thread as if an interrupt had occured.  Only abort
+ * interruptable waits (unfortunately it isn't safe to abort others).
+ *
+ * XXX: What in the world does the comment below mean?
+ * Also, whatever the signal code does...
+ */
+void
+sleepq_abort(struct thread *td)
+{
+	void *wchan;
+
+	mtx_assert(&sched_lock, MA_OWNED);
+	MPASS(TD_ON_SLEEPQ(td));
+	MPASS(td->td_flags & TDF_SINTR);
+
+	/*
+	 * If the TDF_TIMEOUT flag is set, just leave. A
+	 * timeout is scheduled anyhow.
+	 */
+	if (td->td_flags & TDF_TIMEOUT)
+		return;
+
+	CTR3(KTR_PROC, "sleepq_abort: thread %p (pid %d, %s)", td,
+	    td->td_proc->p_pid, td->td_proc->p_comm);
+	wchan = td->td_wchan;
+	mtx_unlock_spin(&sched_lock);
+	sleepq_remove(td, wchan);
+	mtx_lock_spin(&sched_lock);
+}