Messages in this thread Patch in this message | | | From | Joseph Qi <> | Subject | [PATCH v3] psi: get poll_work to run when calling poll syscall next time | Date | Wed, 21 Aug 2019 11:26:25 +0800 |
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From: Jason Xing <kerneljasonxing@linux.alibaba.com>
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.
Signed-off-by: Jason Xing <kerneljasonxing@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> Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com> --- v3: Change the description as Johannes Weiner suggested.
kernel/sched/psi.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 23fbbcc..6e52b67 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -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); -- 1.8.3.1
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