Messages in this thread | | | Subject | Re: [v4.2+ regression] fd7a4bed sched, rt: Convert switched_{from, to}_rt() / prio_changed_rt() to balance callbacks | From | Mike Galbraith <> | Date | Tue, 29 Sep 2015 10:19:51 +0200 |
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On Mon, 2015-09-28 at 04:17 +0200, Mike Galbraith wrote: > Hi Peter, > > I bumped into an odd futextest regression, and finally bisected it to > $subject. I haven't poked at it yet, chasing down and confirming the > little bugger munched the day.
homer:/home/git/futextest/functional # ./futex_requeue_pi -c -b -o -t 500000 -v 2 2>&1|egrep 'exit|Blocker' INFO: Waiter 0: exiting with 0 INFO: Waiter 1: exiting with 0 INFO: Waiter 2: exiting with 0 INFO: Waiter 3: exiting with 0 INFO: Waiter 4: exiting with 0 INFO: Waiter 5: exiting with 0 INFO: Waiter 6: exiting with 0 INFO: Waiter 7: exiting with 0 INFO: Waiter 8: exiting with 0 INFO: Waiter 9: exiting with 0 INFO: Waker: exiting with 0 INFO: Blocker: Calling futex_wait()
Well now, it _seems_ you're innocent Peter. Waker can call futex_wake() before blocker calls futex_wait(), leaving poor blocker stranded.
Adding atomic_inc(&waiters_blocked) to blocker, and telling wakers to expect one more when a blocker exists seems to have fixed it up.
-Mike
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