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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