Commit 7b2b55da authored Aug 24, 2019 by Jason Xing Committed by Linus Torvalds Aug 24, 2019

psi: get poll_work to run when calling poll syscall next time

Only when calling the poll syscall the first time can user receive
POLLPRI correctly.  After that, user always fails to acquire the event
signal.

Reproduce case:
 1. Get the monitor code in Documentation/accounting/psi.txt
 2. Run it, and wait for the event triggered.
 3. Kill and restart the process.

The question is why we can end up with poll_scheduled = 1 but the work
not running (which would reset it to 0).  And the answer is because the
scheduling side sees group->poll_kworker under RCU protection and then
schedules it, but here we cancel the work and destroy the worker.  The
cancel needs to pair with resetting the poll_scheduled flag.

Link: http://lkml.kernel.org/r/1566357985-97781-1-git-send-email-joseph.qi@linux.alibaba.com


Signed-off-by: Jason Xing <kerneljasonxing@linux.alibaba.com>
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Caspar Zhang <caspar@linux.alibaba.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bb65f89b

kernel/sched/psi.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -1131,7 +1131,15 @@ static void psi_trigger_destroy(struct kref *ref)
		* deadlock while waiting for psi_poll_work to acquire trigger_lock
		*/
		if (kworker_to_destroy) {
		/*
		* After the RCU grace period has expired, the worker
		* can no longer be found through group->poll_kworker.
		* But it might have been already scheduled before
		* that - deschedule it cleanly before destroying it.
		*/
		kthread_cancel_delayed_work_sync(&group->poll_work);
		atomic_set(&group->poll_scheduled, 0);

		kthread_destroy_worker(kworker_to_destroy);
		}
		kfree(t);

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