From 7b2b55da1db10a5525460633ae4b6fb0be060c41 Mon Sep 17 00:00:00 2001 From: Jason Xing Date: Sat, 24 Aug 2019 17:54:53 -0700 Subject: [PATCH] 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 Signed-off-by: Joseph Qi Reviewed-by: Caspar Zhang Reviewed-by: Suren Baghdasaryan Acked-by: Johannes Weiner Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/sched/psi.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 23fbbcc414d5..6e52b67b420e 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); -- 2.20.1