kern_condvar.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2000 Jake Burkholder <jake@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.
 *
 * 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.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include "opt_ktrace.h"
 
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/condvar.h>
#include <sys/sched.h>
#include <sys/signalvar.h>
#include <sys/sleepqueue.h>
#include <sys/resourcevar.h>
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif
 
/*
 * A bound below which cv_waiters is valid.  Once cv_waiters reaches this bound,
 * cv_signal must manually check the wait queue for threads.
 */
#define CV_WAITERS_BOUND        INT_MAX
 
#define CV_WAITERS_INC(cvp) do {                                        \
        if ((cvp)->cv_waiters < CV_WAITERS_BOUND)                       \
                (cvp)->cv_waiters++;                                    \
} while (0)
 
/*
 * Common sanity checks for cv_wait* functions.
 */
#define CV_ASSERT(cvp, lock, td) do {                                   \
        KASSERT((td) != NULL, ("%s: td NULL", __func__));               \
        KASSERT(TD_IS_RUNNING(td), ("%s: not TDS_RUNNING", __func__));  \
        KASSERT((cvp) != NULL, ("%s: cvp NULL", __func__));             \
        KASSERT((lock) != NULL, ("%s: lock NULL", __func__));           \
} while (0)
 
/*
 * Initialize a condition variable.  Must be called before use.
 */
void
cv_init(struct cv *cvp, const char *desc)
{
 
        cvp->cv_description = desc;
        cvp->cv_waiters = 0;
}
 
/*
 * Destroy a condition variable.  The condition variable must be re-initialized
 * in order to be re-used.
 */
void
cv_destroy(struct cv *cvp)
{
#ifdef INVARIANTS
        struct sleepqueue *sq;
 
        sleepq_lock(cvp);
        sq = sleepq_lookup(cvp);
        sleepq_release(cvp);
        KASSERT(sq == NULL, ("%s: associated sleep queue non-empty", __func__));
#endif
}
 
/*
 * Wait on a condition variable.  The current thread is placed on the condition
 * variable's wait queue and suspended.  A cv_signal or cv_broadcast on the same
 * condition variable will resume the thread.  The mutex is released before
 * sleeping and will be held on return.  It is recommended that the mutex be
 * held when cv_signal or cv_broadcast are called.
 */
void
_cv_wait(struct cv *cvp, struct lock_object *lock)
{
        WITNESS_SAVE_DECL(lock_witness);
        struct lock_class *class;
        struct thread *td;
        uintptr_t lock_state;
 
        td = curthread;
        lock_state = 0;
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(1, 0, cv_wmesg(cvp));
#endif
        CV_ASSERT(cvp, lock, td);
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
            "Waiting on \"%s\"", cvp->cv_description);
        class = LOCK_CLASS(lock);
 
        if (SCHEDULER_STOPPED_TD(td))
                return;
 
        sleepq_lock(cvp);
 
        CV_WAITERS_INC(cvp);
        if (lock == &Giant.lock_object)
                mtx_assert(&Giant, MA_OWNED);
        DROP_GIANT();
 
        sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
        if (lock != &Giant.lock_object) {
                if (class->lc_flags & LC_SLEEPABLE)
                        sleepq_release(cvp);
                WITNESS_SAVE(lock, lock_witness);
                lock_state = class->lc_unlock(lock);
                if (class->lc_flags & LC_SLEEPABLE)
                        sleepq_lock(cvp);
        }
        sleepq_wait(cvp, 0);
 
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(0, 0, cv_wmesg(cvp));
#endif
        PICKUP_GIANT();
        if (lock != &Giant.lock_object) {
                class->lc_lock(lock, lock_state);
                WITNESS_RESTORE(lock, lock_witness);
        }
}
 
/*
 * Wait on a condition variable.  This function differs from cv_wait by
 * not acquiring the mutex after condition variable was signaled.
 */
void
_cv_wait_unlock(struct cv *cvp, struct lock_object *lock)
{
        struct lock_class *class;
        struct thread *td;
 
        td = curthread;
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(1, 0, cv_wmesg(cvp));
#endif
        CV_ASSERT(cvp, lock, td);
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
            "Waiting on \"%s\"", cvp->cv_description);
        KASSERT(lock != &Giant.lock_object,
            ("cv_wait_unlock cannot be used with Giant"));
        class = LOCK_CLASS(lock);
 
        if (SCHEDULER_STOPPED_TD(td)) {
                class->lc_unlock(lock);
                return;
        }
 
        sleepq_lock(cvp);
 
        CV_WAITERS_INC(cvp);
        DROP_GIANT();
 
        sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
        if (class->lc_flags & LC_SLEEPABLE)
                sleepq_release(cvp);
        class->lc_unlock(lock);
        if (class->lc_flags & LC_SLEEPABLE)
                sleepq_lock(cvp);
        sleepq_wait(cvp, 0);
 
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(0, 0, cv_wmesg(cvp));
#endif
        PICKUP_GIANT();
}
 
/*
 * Wait on a condition variable, allowing interruption by signals.  Return 0 if
 * the thread was resumed with cv_signal or cv_broadcast, EINTR or ERESTART if
 * a signal was caught.  If ERESTART is returned the system call should be
 * restarted if possible.
 */
int
_cv_wait_sig(struct cv *cvp, struct lock_object *lock)
{
        WITNESS_SAVE_DECL(lock_witness);
        struct lock_class *class;
        struct thread *td;
        uintptr_t lock_state;
        int rval;
 
        td = curthread;
        lock_state = 0;
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(1, 0, cv_wmesg(cvp));
#endif
        CV_ASSERT(cvp, lock, td);
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
            "Waiting on \"%s\"", cvp->cv_description);
        class = LOCK_CLASS(lock);
 
        if (SCHEDULER_STOPPED_TD(td))
                return (0);
 
        sleepq_lock(cvp);
 
        CV_WAITERS_INC(cvp);
        if (lock == &Giant.lock_object)
                mtx_assert(&Giant, MA_OWNED);
        DROP_GIANT();
 
        sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
            SLEEPQ_INTERRUPTIBLE, 0);
        if (lock != &Giant.lock_object) {
                if (class->lc_flags & LC_SLEEPABLE)
                        sleepq_release(cvp);
                WITNESS_SAVE(lock, lock_witness);
                lock_state = class->lc_unlock(lock);
                if (class->lc_flags & LC_SLEEPABLE)
                        sleepq_lock(cvp);
        }
        rval = sleepq_wait_sig(cvp, 0);
 
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(0, 0, cv_wmesg(cvp));
#endif
        PICKUP_GIANT();
        if (lock != &Giant.lock_object) {
                class->lc_lock(lock, lock_state);
                WITNESS_RESTORE(lock, lock_witness);
        }
 
        return (rval);
}
 
/*
 * Wait on a condition variable for (at most) the value specified in sbt
 * argument. Returns 0 if the process was resumed by cv_signal or cv_broadcast,
 * EWOULDBLOCK if the timeout expires.
 */
int
_cv_timedwait_sbt(struct cv *cvp, struct lock_object *lock, sbintime_t sbt,
    sbintime_t pr, int flags)
{
        WITNESS_SAVE_DECL(lock_witness);
        struct lock_class *class;
        struct thread *td;
        int lock_state, rval;
 
        td = curthread;
        lock_state = 0;
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(1, 0, cv_wmesg(cvp));
#endif
        CV_ASSERT(cvp, lock, td);
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
            "Waiting on \"%s\"", cvp->cv_description);
        class = LOCK_CLASS(lock);
 
        if (SCHEDULER_STOPPED_TD(td))
                return (0);
 
        sleepq_lock(cvp);
 
        CV_WAITERS_INC(cvp);
        if (lock == &Giant.lock_object)
                mtx_assert(&Giant, MA_OWNED);
        DROP_GIANT();
 
        sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
        sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
        if (lock != &Giant.lock_object) {
                if (class->lc_flags & LC_SLEEPABLE)
                        sleepq_release(cvp);
                WITNESS_SAVE(lock, lock_witness);
                lock_state = class->lc_unlock(lock);
                if (class->lc_flags & LC_SLEEPABLE)
                        sleepq_lock(cvp);
        }
        rval = sleepq_timedwait(cvp, 0);
 
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(0, 0, cv_wmesg(cvp));
#endif
        PICKUP_GIANT();
        if (lock != &Giant.lock_object) {
                class->lc_lock(lock, lock_state);
                WITNESS_RESTORE(lock, lock_witness);
        }
 
        return (rval);
}
 
/*
 * Wait on a condition variable for (at most) the value specified in sbt 
 * argument, allowing interruption by signals.
 * Returns 0 if the thread was resumed by cv_signal or cv_broadcast,
 * EWOULDBLOCK if the timeout expires, and EINTR or ERESTART if a signal
 * was caught.
 */
int
_cv_timedwait_sig_sbt(struct cv *cvp, struct lock_object *lock,
    sbintime_t sbt, sbintime_t pr, int flags)
{
        WITNESS_SAVE_DECL(lock_witness);
        struct lock_class *class;
        struct thread *td;
        int lock_state, rval;
 
        td = curthread;
        lock_state = 0;
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(1, 0, cv_wmesg(cvp));
#endif
        CV_ASSERT(cvp, lock, td);
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
            "Waiting on \"%s\"", cvp->cv_description);
        class = LOCK_CLASS(lock);
 
        if (SCHEDULER_STOPPED_TD(td))
                return (0);
 
        sleepq_lock(cvp);
 
        CV_WAITERS_INC(cvp);
        if (lock == &Giant.lock_object)
                mtx_assert(&Giant, MA_OWNED);
        DROP_GIANT();
 
        sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
            SLEEPQ_INTERRUPTIBLE, 0);
        sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
        if (lock != &Giant.lock_object) {
                if (class->lc_flags & LC_SLEEPABLE)
                        sleepq_release(cvp);
                WITNESS_SAVE(lock, lock_witness);
                lock_state = class->lc_unlock(lock);
                if (class->lc_flags & LC_SLEEPABLE)
                        sleepq_lock(cvp);
        }
        rval = sleepq_timedwait_sig(cvp, 0);
 
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(0, 0, cv_wmesg(cvp));
#endif
        PICKUP_GIANT();
        if (lock != &Giant.lock_object) {
                class->lc_lock(lock, lock_state);
                WITNESS_RESTORE(lock, lock_witness);
        }
 
        return (rval);
}
 
/*
 * Signal a condition variable, wakes up one waiting thread.  Will also wakeup
 * the swapper if the process is not in memory, so that it can bring the
 * sleeping process in.  Note that this may also result in additional threads
 * being made runnable.  Should be called with the same mutex as was passed to
 * cv_wait held.
 */
void
cv_signal(struct cv *cvp)
{
 
        if (cvp->cv_waiters == 0)
                return;
        sleepq_lock(cvp);
        if (cvp->cv_waiters == 0) {
                sleepq_release(cvp);
                return;
        }
        if (cvp->cv_waiters == CV_WAITERS_BOUND && sleepq_lookup(cvp) == NULL) {
                cvp->cv_waiters = 0;
                sleepq_release(cvp);
        } else {
                if (cvp->cv_waiters < CV_WAITERS_BOUND)
                        cvp->cv_waiters--;
                if (sleepq_signal(cvp, SLEEPQ_CONDVAR | SLEEPQ_DROP, 0, 0))
                        kick_proc0();
        }
}
 
/*
 * Broadcast a signal to a condition variable.  Wakes up all waiting threads.
 * Should be called with the same mutex as was passed to cv_wait held.
 */
void
cv_broadcastpri(struct cv *cvp, int pri)
{
        int wakeup_swapper;
 
        if (cvp->cv_waiters == 0)
                return;
        /*
         * XXX sleepq_broadcast pri argument changed from -1 meaning
         * no pri to 0 meaning no pri.
         */
        wakeup_swapper = 0;
        if (pri == -1)
                pri = 0;
        sleepq_lock(cvp);
        if (cvp->cv_waiters > 0) {
                cvp->cv_waiters = 0;
                wakeup_swapper = sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0);
        }
        sleepq_release(cvp);
        if (wakeup_swapper)
                kick_proc0();
}