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@linux.vnet.ibm.com
Fixes: 9cd75c3cd4c3d ("userfaultfd: non-cooperative: add ability to report
non-PF events from uffd descriptor")
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 2d8c2d848668076111daf445098fdf182aa6c9e6..06ea26b8c996f3cc7a9d6fd177260f89394fb325 100644 (file)
--- a/fs/userfaultfd.c
+++ b/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;