cvs commit: src/sys/kern subr_sleepqueue.c
jhb at FreeBSD.org
Wed Apr 13 23:30:33 PDT 2005
jhb 2005-04-14 06:30:32 UTC
FreeBSD src repository
Close a race between sleepq_broadcast() and sleepq_catch_signals().
Specifically, sleepq_broadcast() uses td_slpq for its private pending
queue of threads that it is going to wake up after it takes them off the
sleep queue. The problem is that if one of the threads is actually not
asleep yet, then we can end up with td_slpq being corrupted and/or the
thread being made runnable at the wrong time resulting in the td_sleepqueue
== NULL assertion failures occasionally reported under heavy load.
The fix is to stop being so fancy and ditch the whole pending queue bit.
Instead, sleepq_remove_thread() and sleepq_resume_thread() were merged
into one function that requires the caller to hold sched_lock. This
fixes several places that unlocked sched_lock only to call a function
that then locked sched_lock, so even though sched_lock is now held
slightly longer, removing the extra lock acquires (1 pair instead of 3
in some cases) probably makes it an overall win if you don't include the
fact that it closes a race. This is definitely a 5.4 candidate.
Submitted by: Steven Sears stevenjsears at yahoo dot com
MFC after: 4 days
Revision Changes Path
1.17 +21 -47 src/sys/kern/subr_sleepqueue.c
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