From: Jason Xing kerneljasonxing@linux.alibaba.com Subject: 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.a... 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 ---

kernel/sched/psi.c | 8 ++++++++ 1 file changed, 8 insertions(+)

--- a/kernel/sched/psi.c~psi-get-poll_work-to-run-when-calling-poll-syscall-next-time +++ a/kernel/sched/psi.c @@ -1131,7 +1131,15 @@ static void psi_trigger_destroy(struct k * 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); _