95b66e9e53
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. PR: kern/79693 Submitted by: Steven Sears stevenjsears at yahoo dot com MFC after: 4 days
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