Author: markj
Date: Thu Dec 22 17:51:44 2016
New Revision: 310423
URL: https://svnweb.freebsd.org/changeset/base/310423
Log:
Revert part of r300109.
The removal of TAILQ_FOREACH_SAFE introduced a small race: when the last
thread on a sleepqueue is awoken, it reclaims the sleepqueue and may begin
executing on a different CPU before sleepq_resume_thread() returns. This
leaves a window during which it may go back to sleep and incorrectly be
awoken again by the caller of sleepq_broadcast().
Reported and tested by: pho
MFC after: 3 days
Sponsored by: Dell EMC Isilon
Modified:
head/sys/kern/subr_sleepqueue.c
Modified: head/sys/kern/subr_sleepqueue.c
==============================================================================
--- head/sys/kern/subr_sleepqueue.c Thu Dec 22 17:44:27 2016
(r310422)
+++ head/sys/kern/subr_sleepqueue.c Thu Dec 22 17:51:44 2016
(r310423)
@@ -880,7 +880,7 @@ int
sleepq_broadcast(void *wchan, int flags, int pri, int queue)
{
struct sleepqueue *sq;
- struct thread *td;
+ struct thread *td, *tdn;
int wakeup_swapper;
CTR2(KTR_PROC, "sleepq_broadcast(%p, %d)", wchan, flags);
@@ -894,7 +894,7 @@ sleepq_broadcast(void *wchan, int flags,
/* Resume all blocked threads on the sleep queue. */
wakeup_swapper = 0;
- while ((td = TAILQ_FIRST(&sq->sq_blocked[queue])) != NULL) {
+ TAILQ_FOREACH_SAFE(td, &sq->sq_blocked[queue], td_slpq, tdn) {
thread_lock(td);
wakeup_swapper |= sleepq_resume_thread(sq, td, pri);
thread_unlock(td);
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