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| /freebsd-10.1-release/sys/kern/ | ||
| H A D | subr_sleepqueue.c | diff 175654 Fri Jan 25 00:09:38 MST 2008 jhb Fix a race in the sleepqueue timeout code that resulted in sleeps not being properly cancelled by a timeout. In general there is a race between a the sleepq timeout handler firing while the thread is still in the process of going to sleep. In 6.x with sched_lock, the race was largely protected by sched_lock. The only place it was "exposed" and had to be handled was while checking for any pending signals in sleepq_catch_signals(). With the thread lock changes, the thread lock is dropped in between sleepq_add() and sleepq_*wait*() opening up a new window for this race. Thus, if the timeout fired while the sleeping thread was in between sleepq_add() and sleepq_*wait*(), the thread would be marked as timed out, but the thread would not be dequeued and sleepq_switch() would still block the thread until it was awakened via some other means. In the case of pause(9) where there is no other wakeup, the thread would never be awakened. Fix this by teaching sleepq_switch() to check if the thread has had its sleep canceled before blocking by checking the TDF_TIMEOUT flag and aborting the sleep and dequeueing the thread if it is set. MFC after: 3 days Reported by: dwhite, peter |
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