[patch 14/16] userfaultfd: non-cooperative: flush event_wqh at release time

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From: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Subject: userfaultfd: non-cooperative: flush event_wqh at release time

There may still be threads waiting on event_wqh at the time the userfault
file descriptor is closed.  Flush the events wait-queue to prevent waiting
threads from hanging.

Link: http://lkml.kernel.org/r/1501398127-30419-1-git-send-email-rppt@xxxxxxxxxxxxxxxxxx
Fixes: 9cd75c3cd4c3d ("userfaultfd: non-cooperative: add ability to report
non-PF events from uffd descriptor")
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/userfaultfd.c |    3 +++
 1 file changed, 3 insertions(+)

diff -puN fs/userfaultfd.c~userfaultfd-non-cooperative-flush-event_wqh-at-release-time fs/userfaultfd.c
--- a/fs/userfaultfd.c~userfaultfd-non-cooperative-flush-event_wqh-at-release-time
+++ a/fs/userfaultfd.c
@@ -854,6 +854,9 @@ wakeup:
 	__wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
 	spin_unlock(&ctx->fault_pending_wqh.lock);
 
+	/* Flush pending events that may still wait on event_wqh */
+	wake_up_all(&ctx->event_wqh);
+
 	wake_up_poll(&ctx->fd_wqh, POLLHUP);
 	userfaultfd_ctx_put(ctx);
 	return 0;
_



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