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    Subject[PATCH 4.12 021/106] userfaultfd: non-cooperative: flush event_wqh at release time
    Date
    4.12-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mike Rapoport <rppt@linux.vnet.ibm.com>

    commit 5a18b64e3f02125be1c0ef777501ae38aafe2a24 upstream.

    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>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

    --- a/fs/userfaultfd.c
    +++ b/fs/userfaultfd.c
    @@ -851,6 +851,9 @@ 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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