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freebsd/sys/kern/subr_sleepqueue.c
John Baldwin 95b66e9e53 Close a race between sleepq_broadcast() and sleepq_catch_signals().
Specifically, sleepq_broadcast() uses td_slpq for its private pending
queue of threads that it is going to wake up after it takes them off the
sleep queue.  The problem is that if one of the threads is actually not
asleep yet, then we can end up with td_slpq being corrupted and/or the
thread being made runnable at the wrong time resulting in the td_sleepqueue
== NULL assertion failures occasionally reported under heavy load.

The fix is to stop being so fancy and ditch the whole pending queue bit.
Instead, sleepq_remove_thread() and sleepq_resume_thread() were merged
into one function that requires the caller to hold sched_lock.  This
fixes several places that unlocked sched_lock only to call a function
that then locked sched_lock, so even though sched_lock is now held
slightly longer, removing the extra lock acquires (1 pair instead of 3
in some cases) probably makes it an overall win if you don't include the
fact that it closes a race.  This is definitely a 5.4 candidate.

PR:		kern/79693
Submitted by:	Steven Sears stevenjsears at yahoo dot com
MFC after:	4 days
2005-04-14 06:30:32 +00:00

845 lines
24 KiB
C

/*-
* 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 "opt_sleepqueue_profiling.h"
#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>
#include <sys/sysctl.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. */
#ifdef INVARIANTS
int sq_type; /* (c) Queue type. */
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. */
#ifdef SLEEPQUEUE_PROFILING
u_int sc_depth; /* Length of sc_queues. */
u_int sc_max_depth; /* Max length of sc_queues. */
#endif
};
#ifdef SLEEPQUEUE_PROFILING
u_int sleepq_max_depth;
SYSCTL_NODE(_debug, OID_AUTO, sleepq, CTLFLAG_RD, 0, "sleepq profiling");
SYSCTL_NODE(_debug_sleepq, OID_AUTO, chains, CTLFLAG_RD, 0,
"sleepq chain stats");
SYSCTL_UINT(_debug_sleepq, OID_AUTO, max_depth, CTLFLAG_RD, &sleepq_max_depth,
0, "maxmimum depth achieved of a single chain");
#endif
static struct sleepqueue_chain sleepq_chains[SC_TABLESIZE];
static 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_resume_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)
{
#ifdef SLEEPQUEUE_PROFILING
struct sysctl_oid *chain_oid;
char chain_name[10];
#endif
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);
#ifdef SLEEPQUEUE_PROFILING
snprintf(chain_name, sizeof(chain_name), "%d", i);
chain_oid = SYSCTL_ADD_NODE(NULL,
SYSCTL_STATIC_CHILDREN(_debug_sleepq_chains), OID_AUTO,
chain_name, CTLFLAG_RD, NULL, "sleepq chain stats");
SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
"depth", CTLFLAG_RD, &sleepq_chains[i].sc_depth, 0, NULL);
SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
"max_depth", CTLFLAG_RD, &sleepq_chains[i].sc_max_depth, 0,
NULL);
#endif
}
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);
}
/*
* Lock the sleep queue chain associated with the specified wait channel.
*/
void
sleepq_lock(void *wchan)
{
struct sleepqueue_chain *sc;
sc = SC_LOOKUP(wchan);
mtx_lock_spin(&sc->sc_lock);
}
/*
* Look up the sleep queue associated with a given wait channel in the hash
* table locking the associated sleep queue chain. 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_assert(&sc->sc_lock, MA_OWNED);
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 sleep queue 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(void *wchan, struct mtx *lock, const char *wmesg, int flags)
{
struct sleepqueue_chain *sc;
struct sleepqueue *sq;
struct thread *td;
td = curthread;
sc = SC_LOOKUP(wchan);
mtx_assert(&sc->sc_lock, MA_OWNED);
MPASS(td->td_sleepqueue != NULL);
MPASS(wchan != NULL);
/* Look up the sleep queue associated with the wait channel 'wchan'. */
sq = sleepq_lookup(wchan);
/*
* If the wait channel does not already have a sleep queue, use
* this thread's sleep queue. Otherwise, insert the current thread
* into the sleep queue already in use by this wait channel.
*/
if (sq == NULL) {
#ifdef SLEEPQUEUE_PROFILING
sc->sc_depth++;
if (sc->sc_depth > sc->sc_max_depth) {
sc->sc_max_depth = sc->sc_depth;
if (sc->sc_max_depth > sleepq_max_depth)
sleepq_max_depth = sc->sc_max_depth;
}
#endif
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;
sq->sq_type = flags & SLEEPQ_TYPE;
#endif
} else {
MPASS(wchan == sq->sq_wchan);
MPASS(lock == sq->sq_lock);
MPASS((flags & SLEEPQ_TYPE) == sq->sq_type);
LIST_INSERT_HEAD(&sq->sq_free, td->td_sleepqueue, sq_hash);
}
TAILQ_INSERT_TAIL(&sq->sq_blocked, td, td_slpq);
td->td_sleepqueue = NULL;
mtx_lock_spin(&sched_lock);
td->td_wchan = wchan;
td->td_wmesg = wmesg;
if (flags & SLEEPQ_INTERRUPTIBLE)
td->td_flags |= TDF_SINTR;
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(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 do_upcall;
int sig;
do_upcall = 0;
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 %ld, %s)",
(void *)td, (long)p->p_pid, p->p_comm);
/* Mark thread as being in an interruptible sleep. */
MPASS(td->td_flags & TDF_SINTR);
MPASS(TD_ON_SLEEPQ(td));
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;
else
do_upcall = thread_upcall_check(td);
PROC_UNLOCK(p);
/*
* If there were pending signals and this thread is still on
* the sleep queue, remove it from the sleep queue. If the
* thread was removed from the sleep queue while we were blocked
* above, then clear TDF_SINTR before returning.
*/
sleepq_lock(wchan);
sq = sleepq_lookup(wchan);
mtx_lock_spin(&sched_lock);
if (TD_ON_SLEEPQ(td) && (sig != 0 || do_upcall != 0))
sleepq_resume_thread(sq, td, -1);
else if (!TD_ON_SLEEPQ(td) && sig == 0)
td->td_flags &= ~TDF_SINTR;
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 sleep queue 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, NULL);
KASSERT(TD_IS_RUNNING(td), ("running but not TDS_RUNNING"));
CTR3(KTR_PROC, "sleepq resume: thread %p (pid %ld, %s)",
(void *)td, (long)td->td_proc->p_pid, (void *)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, NULL);
}
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;
/*
* If TDF_SINTR is clear, then we were awakened while executing
* sleepq_catch_signals().
*/
if (!(td->td_flags & TDF_SINTR))
return (0);
/* We are no longer in an interruptible sleep. */
td->td_flags &= ~TDF_SINTR;
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)
{
MPASS(!(curthread->td_flags & TDF_SINTR));
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 rval;
MPASS(!(curthread->td_flags & TDF_SINTR));
sleepq_switch(wchan);
rval = sleepq_check_timeout();
mtx_unlock_spin(&sched_lock);
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 makes it
* runnable.
*/
static void
sleepq_resume_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);
mtx_assert(&sched_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
#ifdef SLEEPQUEUE_PROFILING
sc->sc_depth--;
#endif
} else
td->td_sleepqueue = LIST_FIRST(&sq->sq_free);
LIST_REMOVE(td->td_sleepqueue, sq_hash);
td->td_wmesg = NULL;
td->td_wchan = NULL;
/*
* Note that thread td might not be sleeping if it is running
* sleepq_catch_signals() on another CPU or is blocked on
* its proc lock to check signals. It doesn't hurt to clear
* the sleeping flag if it isn't set though, so we just always
* do it. However, we can't assert that it is set.
*/
CTR3(KTR_PROC, "sleepq_wakeup: thread %p (pid %ld, %s)",
(void *)td, (long)td->td_proc->p_pid, td->td_proc->p_comm);
TD_CLR_SLEEPING(td);
/* Adjust priority if requested. */
MPASS(pri == -1 || (pri >= PRI_MIN && pri <= PRI_MAX));
if (pri != -1 && td->td_priority > pri)
sched_prio(td, pri);
setrunnable(td);
}
/*
* 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;
struct thread *td, *besttd;
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_type == (flags & SLEEPQ_TYPE),
("%s: mismatch between sleep/wakeup and cv_*", __func__));
/*
* Find the highest priority thread on the queue. If there is a
* tie, use the thread that first appears in the queue as it has
* been sleeping the longest since threads are always added to
* the tail of sleep queues.
*/
besttd = NULL;
TAILQ_FOREACH(td, &sq->sq_blocked, td_slpq) {
if (besttd == NULL || td->td_priority < besttd->td_priority)
besttd = td;
}
MPASS(besttd != NULL);
mtx_lock_spin(&sched_lock);
sleepq_resume_thread(sq, besttd, pri);
mtx_unlock_spin(&sched_lock);
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_type == (flags & SLEEPQ_TYPE),
("%s: mismatch between sleep/wakeup and cv_*", __func__));
/* Resume all blocked threads on the sleep queue. */
mtx_lock_spin(&sched_lock);
while (!TAILQ_EMPTY(&sq->sq_blocked))
sleepq_resume_thread(sq, TAILQ_FIRST(&sq->sq_blocked), pri);
mtx_unlock_spin(&sched_lock);
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 = arg;
CTR3(KTR_PROC, "sleepq_timeout: thread %p (pid %ld, %s)",
(void *)td, (long)td->td_proc->p_pid, (void *)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);
sleepq_lock(wchan);
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->td_wchan == wchan);
MPASS(sq != NULL);
td->td_flags |= TDF_TIMEOUT;
sleepq_resume_thread(sq, td, -1);
mtx_unlock_spin(&sched_lock);
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) {
MPASS(TD_IS_SLEEPING(td));
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);
sleepq_lock(wchan);
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;
}
MPASS(sq != NULL);
/* Thread is asleep on sleep queue sq, so wake it up. */
sleepq_resume_thread(sq, td, -1);
sleepq_release(wchan);
mtx_unlock_spin(&sched_lock);
}
/*
* Abort a thread as if an interrupt had occurred. Only abort
* interruptible 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 %ld, %s)",
(void *)td, (long)td->td_proc->p_pid, (void *)td->td_proc->p_comm);
wchan = td->td_wchan;
mtx_unlock_spin(&sched_lock);
sleepq_remove(td, wchan);
mtx_lock_spin(&sched_lock);
}