Author: markj
Date: Tue Jan 26 00:22:02 2016
New Revision: 294755
URL: https://svnweb.freebsd.org/changeset/base/294755
Log:
MFC r293458:
Prevent cv_waiters wraparound.
Modified:
stable/10/sys/kern/kern_condvar.c
Directory Properties:
stable/10/ (props changed)
Modified: stable/10/sys/kern/kern_condvar.c
==============================================================================
--- stable/10/sys/kern/kern_condvar.c Mon Jan 25 23:04:40 2016
(r294754)
+++ stable/10/sys/kern/kern_condvar.c Tue Jan 26 00:22:02 2016
(r294755)
@@ -31,6 +31,7 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
+#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
@@ -47,6 +48,17 @@ __FBSDID("$FreeBSD$");
#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 {
\
@@ -122,7 +134,7 @@ _cv_wait(struct cv *cvp, struct lock_obj
sleepq_lock(cvp);
- cvp->cv_waiters++;
+ CV_WAITERS_INC(cvp);
if (lock == &Giant.lock_object)
mtx_assert(&Giant, MA_OWNED);
DROP_GIANT();
@@ -184,7 +196,7 @@ _cv_wait_unlock(struct cv *cvp, struct l
sleepq_lock(cvp);
- cvp->cv_waiters++;
+ CV_WAITERS_INC(cvp);
DROP_GIANT();
sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
@@ -240,7 +252,7 @@ _cv_wait_sig(struct cv *cvp, struct lock
sleepq_lock(cvp);
- cvp->cv_waiters++;
+ CV_WAITERS_INC(cvp);
if (lock == &Giant.lock_object)
mtx_assert(&Giant, MA_OWNED);
DROP_GIANT();
@@ -307,7 +319,7 @@ _cv_timedwait_sbt(struct cv *cvp, struct
sleepq_lock(cvp);
- cvp->cv_waiters++;
+ CV_WAITERS_INC(cvp);
if (lock == &Giant.lock_object)
mtx_assert(&Giant, MA_OWNED);
DROP_GIANT();
@@ -376,7 +388,7 @@ _cv_timedwait_sig_sbt(struct cv *cvp, st
sleepq_lock(cvp);
- cvp->cv_waiters++;
+ CV_WAITERS_INC(cvp);
if (lock == &Giant.lock_object)
mtx_assert(&Giant, MA_OWNED);
DROP_GIANT();
@@ -422,8 +434,15 @@ cv_signal(struct cv *cvp)
wakeup_swapper = 0;
sleepq_lock(cvp);
if (cvp->cv_waiters > 0) {
- cvp->cv_waiters--;
- wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0, 0);
+ if (cvp->cv_waiters == CV_WAITERS_BOUND &&
+ sleepq_lookup(cvp) == NULL) {
+ cvp->cv_waiters = 0;
+ } else {
+ if (cvp->cv_waiters < CV_WAITERS_BOUND)
+ cvp->cv_waiters--;
+ wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0,
+ 0);
+ }
}
sleepq_release(cvp);
if (wakeup_swapper)
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