5c894ee2ef
thread awakened due to a time out, then cv_waiters was not decremented. If INT_MAX threads timed out on a cv without an intervening cv_broadcast, then cv_waiters could overflow. To fix this, have each sleeping thread decrement cv_waiters when it resumes. Note that previously cv_waiters was protected by the sleepq chain lock. However, that lock is not held when threads resume from sleep. In addition, the interlock is also not always reacquired after resuming (cv_wait_unlock), nor is it always held by callers of cv_signal() or cv_broadcast(). Instead, use atomic ops to update cv_waiters. Since the sleepq chain lock is still held on every increment, it should still be safe to compare cv_waiters against zero while holding the lock in the wakeup routines as the only way the race should be lost would result in extra calls to sleepq_signal() or sleepq_broadcast(). Differential Revision: https://reviews.freebsd.org/D2427 Reviewed by: benno Reported by: benno (wrap of cv_waiters in the field) MFC after: 2 weeks
459 lines
12 KiB
C
459 lines
12 KiB
C
/*-
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* Copyright (c) 2000 Jake Burkholder <jake@freebsd.org>.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "opt_ktrace.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/proc.h>
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#include <sys/kernel.h>
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#include <sys/ktr.h>
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#include <sys/condvar.h>
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#include <sys/sched.h>
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#include <sys/signalvar.h>
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#include <sys/sleepqueue.h>
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#include <sys/resourcevar.h>
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#ifdef KTRACE
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#include <sys/uio.h>
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#include <sys/ktrace.h>
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#endif
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/*
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* Common sanity checks for cv_wait* functions.
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*/
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#define CV_ASSERT(cvp, lock, td) do { \
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KASSERT((td) != NULL, ("%s: td NULL", __func__)); \
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KASSERT(TD_IS_RUNNING(td), ("%s: not TDS_RUNNING", __func__)); \
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KASSERT((cvp) != NULL, ("%s: cvp NULL", __func__)); \
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KASSERT((lock) != NULL, ("%s: lock NULL", __func__)); \
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} while (0)
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/*
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* Initialize a condition variable. Must be called before use.
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*/
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void
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cv_init(struct cv *cvp, const char *desc)
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{
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cvp->cv_description = desc;
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cvp->cv_waiters = 0;
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}
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/*
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* Destroy a condition variable. The condition variable must be re-initialized
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* in order to be re-used.
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*/
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void
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cv_destroy(struct cv *cvp)
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{
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#ifdef INVARIANTS
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struct sleepqueue *sq;
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sleepq_lock(cvp);
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sq = sleepq_lookup(cvp);
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sleepq_release(cvp);
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KASSERT(sq == NULL, ("%s: associated sleep queue non-empty", __func__));
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#endif
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}
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/*
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* Wait on a condition variable. The current thread is placed on the condition
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* variable's wait queue and suspended. A cv_signal or cv_broadcast on the same
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* condition variable will resume the thread. The mutex is released before
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* sleeping and will be held on return. It is recommended that the mutex be
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* held when cv_signal or cv_broadcast are called.
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*/
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void
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_cv_wait(struct cv *cvp, struct lock_object *lock)
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{
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WITNESS_SAVE_DECL(lock_witness);
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struct lock_class *class;
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struct thread *td;
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uintptr_t lock_state;
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td = curthread;
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lock_state = 0;
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(1, 0, cv_wmesg(cvp));
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#endif
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CV_ASSERT(cvp, lock, td);
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WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
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"Waiting on \"%s\"", cvp->cv_description);
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class = LOCK_CLASS(lock);
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if (cold || panicstr) {
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/*
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* During autoconfiguration, just give interrupts
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* a chance, then just return. Don't run any other
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* thread or panic below, in case this is the idle
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* process and already asleep.
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*/
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return;
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}
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sleepq_lock(cvp);
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atomic_add_int(&cvp->cv_waiters, 1);
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if (lock == &Giant.lock_object)
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mtx_assert(&Giant, MA_OWNED);
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DROP_GIANT();
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sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
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if (lock != &Giant.lock_object) {
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_release(cvp);
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WITNESS_SAVE(lock, lock_witness);
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lock_state = class->lc_unlock(lock);
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_lock(cvp);
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}
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sleepq_wait(cvp, 0);
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atomic_subtract_int(&cvp->cv_waiters, 1);
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(0, 0, cv_wmesg(cvp));
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#endif
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PICKUP_GIANT();
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if (lock != &Giant.lock_object) {
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class->lc_lock(lock, lock_state);
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WITNESS_RESTORE(lock, lock_witness);
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}
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}
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/*
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* Wait on a condition variable. This function differs from cv_wait by
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* not aquiring the mutex after condition variable was signaled.
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*/
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void
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_cv_wait_unlock(struct cv *cvp, struct lock_object *lock)
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{
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struct lock_class *class;
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struct thread *td;
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td = curthread;
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(1, 0, cv_wmesg(cvp));
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#endif
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CV_ASSERT(cvp, lock, td);
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WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
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"Waiting on \"%s\"", cvp->cv_description);
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KASSERT(lock != &Giant.lock_object,
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("cv_wait_unlock cannot be used with Giant"));
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class = LOCK_CLASS(lock);
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if (cold || panicstr) {
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/*
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* During autoconfiguration, just give interrupts
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* a chance, then just return. Don't run any other
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* thread or panic below, in case this is the idle
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* process and already asleep.
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*/
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class->lc_unlock(lock);
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return;
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}
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sleepq_lock(cvp);
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atomic_add_int(&cvp->cv_waiters, 1);
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DROP_GIANT();
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sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_release(cvp);
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class->lc_unlock(lock);
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_lock(cvp);
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sleepq_wait(cvp, 0);
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atomic_subtract_int(&cvp->cv_waiters, 1);
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(0, 0, cv_wmesg(cvp));
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#endif
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PICKUP_GIANT();
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}
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/*
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* Wait on a condition variable, allowing interruption by signals. Return 0 if
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* the thread was resumed with cv_signal or cv_broadcast, EINTR or ERESTART if
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* a signal was caught. If ERESTART is returned the system call should be
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* restarted if possible.
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*/
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int
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_cv_wait_sig(struct cv *cvp, struct lock_object *lock)
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{
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WITNESS_SAVE_DECL(lock_witness);
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struct lock_class *class;
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struct thread *td;
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uintptr_t lock_state;
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int rval;
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td = curthread;
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lock_state = 0;
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(1, 0, cv_wmesg(cvp));
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#endif
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CV_ASSERT(cvp, lock, td);
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WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
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"Waiting on \"%s\"", cvp->cv_description);
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class = LOCK_CLASS(lock);
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if (cold || panicstr) {
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/*
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* After a panic, or during autoconfiguration, just give
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* interrupts a chance, then just return; don't run any other
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* procs or panic below, in case this is the idle process and
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* already asleep.
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*/
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return (0);
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}
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sleepq_lock(cvp);
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atomic_add_int(&cvp->cv_waiters, 1);
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if (lock == &Giant.lock_object)
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mtx_assert(&Giant, MA_OWNED);
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DROP_GIANT();
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sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
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SLEEPQ_INTERRUPTIBLE, 0);
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if (lock != &Giant.lock_object) {
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_release(cvp);
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WITNESS_SAVE(lock, lock_witness);
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lock_state = class->lc_unlock(lock);
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_lock(cvp);
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}
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rval = sleepq_wait_sig(cvp, 0);
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atomic_subtract_int(&cvp->cv_waiters, 1);
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(0, 0, cv_wmesg(cvp));
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#endif
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PICKUP_GIANT();
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if (lock != &Giant.lock_object) {
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class->lc_lock(lock, lock_state);
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WITNESS_RESTORE(lock, lock_witness);
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}
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return (rval);
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}
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/*
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* Wait on a condition variable for (at most) the value specified in sbt
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* argument. Returns 0 if the process was resumed by cv_signal or cv_broadcast,
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* EWOULDBLOCK if the timeout expires.
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*/
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int
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_cv_timedwait_sbt(struct cv *cvp, struct lock_object *lock, sbintime_t sbt,
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sbintime_t pr, int flags)
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{
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WITNESS_SAVE_DECL(lock_witness);
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struct lock_class *class;
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struct thread *td;
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int lock_state, rval;
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td = curthread;
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lock_state = 0;
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(1, 0, cv_wmesg(cvp));
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#endif
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CV_ASSERT(cvp, lock, td);
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WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
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"Waiting on \"%s\"", cvp->cv_description);
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class = LOCK_CLASS(lock);
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if (cold || panicstr) {
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/*
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* After a panic, or during autoconfiguration, just give
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* interrupts a chance, then just return; don't run any other
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* thread or panic below, in case this is the idle process and
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* already asleep.
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*/
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return 0;
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}
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sleepq_lock(cvp);
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atomic_add_int(&cvp->cv_waiters, 1);
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if (lock == &Giant.lock_object)
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mtx_assert(&Giant, MA_OWNED);
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DROP_GIANT();
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sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
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sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
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if (lock != &Giant.lock_object) {
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_release(cvp);
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WITNESS_SAVE(lock, lock_witness);
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lock_state = class->lc_unlock(lock);
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_lock(cvp);
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}
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rval = sleepq_timedwait(cvp, 0);
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atomic_subtract_int(&cvp->cv_waiters, 1);
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(0, 0, cv_wmesg(cvp));
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#endif
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PICKUP_GIANT();
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if (lock != &Giant.lock_object) {
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class->lc_lock(lock, lock_state);
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WITNESS_RESTORE(lock, lock_witness);
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}
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return (rval);
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}
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/*
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* Wait on a condition variable for (at most) the value specified in sbt
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* argument, allowing interruption by signals.
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* Returns 0 if the thread was resumed by cv_signal or cv_broadcast,
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* EWOULDBLOCK if the timeout expires, and EINTR or ERESTART if a signal
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* was caught.
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*/
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int
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_cv_timedwait_sig_sbt(struct cv *cvp, struct lock_object *lock,
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sbintime_t sbt, sbintime_t pr, int flags)
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{
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WITNESS_SAVE_DECL(lock_witness);
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struct lock_class *class;
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struct thread *td;
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int lock_state, rval;
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td = curthread;
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lock_state = 0;
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(1, 0, cv_wmesg(cvp));
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#endif
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CV_ASSERT(cvp, lock, td);
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WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
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"Waiting on \"%s\"", cvp->cv_description);
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class = LOCK_CLASS(lock);
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if (cold || panicstr) {
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/*
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* After a panic, or during autoconfiguration, just give
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* interrupts a chance, then just return; don't run any other
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* thread or panic below, in case this is the idle process and
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* already asleep.
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*/
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return 0;
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}
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sleepq_lock(cvp);
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atomic_add_int(&cvp->cv_waiters, 1);
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if (lock == &Giant.lock_object)
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mtx_assert(&Giant, MA_OWNED);
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DROP_GIANT();
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sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
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SLEEPQ_INTERRUPTIBLE, 0);
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sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
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if (lock != &Giant.lock_object) {
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_release(cvp);
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WITNESS_SAVE(lock, lock_witness);
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lock_state = class->lc_unlock(lock);
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if (class->lc_flags & LC_SLEEPABLE)
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sleepq_lock(cvp);
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}
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rval = sleepq_timedwait_sig(cvp, 0);
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atomic_subtract_int(&cvp->cv_waiters, 1);
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#ifdef KTRACE
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if (KTRPOINT(td, KTR_CSW))
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ktrcsw(0, 0, cv_wmesg(cvp));
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#endif
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PICKUP_GIANT();
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if (lock != &Giant.lock_object) {
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class->lc_lock(lock, lock_state);
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WITNESS_RESTORE(lock, lock_witness);
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}
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return (rval);
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}
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/*
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* Signal a condition variable, wakes up one waiting thread. Will also wakeup
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* the swapper if the process is not in memory, so that it can bring the
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* sleeping process in. Note that this may also result in additional threads
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* being made runnable. Should be called with the same mutex as was passed to
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* cv_wait held.
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*/
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void
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cv_signal(struct cv *cvp)
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{
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int wakeup_swapper;
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wakeup_swapper = 0;
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sleepq_lock(cvp);
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if (cvp->cv_waiters > 0)
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wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0, 0);
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sleepq_release(cvp);
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if (wakeup_swapper)
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kick_proc0();
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}
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/*
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* Broadcast a signal to a condition variable. Wakes up all waiting threads.
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* Should be called with the same mutex as was passed to cv_wait held.
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*/
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void
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cv_broadcastpri(struct cv *cvp, int pri)
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{
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int wakeup_swapper;
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/*
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* XXX sleepq_broadcast pri argument changed from -1 meaning
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* no pri to 0 meaning no pri.
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*/
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wakeup_swapper = 0;
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if (pri == -1)
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pri = 0;
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sleepq_lock(cvp);
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if (cvp->cv_waiters > 0)
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wakeup_swapper = sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0);
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sleepq_release(cvp);
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if (wakeup_swapper)
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kick_proc0();
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}
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