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authorJason Xing <kerneljasonxing@linux.alibaba.com>2019-08-25 00:54:53 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2019-08-25 02:48:42 (GMT)
commit7b2b55da1db10a5525460633ae4b6fb0be060c41 (patch)
tree877d7e5496c0adc49a978df982522aaeb5e08f51
parentbb65f89b7d3d305c14951f49860711fbcae70692 (diff)
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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>
-rw-r--r--kernel/sched/psi.c8
1 files changed, 8 insertions, 0 deletions
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);