svn commit: r293458 - head/sys/kern
Mark Johnston
markj at FreeBSD.org
Sat Jan 9 01:56:47 UTC 2016
Author: markj
Date: Sat Jan 9 01:56:46 2016
New Revision: 293458
URL: https://svnweb.freebsd.org/changeset/base/293458
Log:
Prevent cv_waiters wraparound.
r282971 attempted to fix this problem by decrementing cv_waiters after
waking up from sleeping on a condition variable, but this can result in
a use-after-free if the CV is freed before all woken threads have had a
chance to run. Instead, avoid incrementing cv_waiters past INT_MAX, and
have cv_signal() explicitly check for sleeping threads once cv_waiters has
reached this bound.
Reviewed by: jhb
MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Division
Differential Revision: https://reviews.freebsd.org/D4822
Modified:
head/sys/kern/kern_condvar.c
Modified: head/sys/kern/kern_condvar.c
==============================================================================
--- head/sys/kern/kern_condvar.c Sat Jan 9 01:43:53 2016 (r293457)
+++ head/sys/kern/kern_condvar.c Sat Jan 9 01:56:46 2016 (r293458)
@@ -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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