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    Subject[2.6.20.16 review 10/28] rt-mutex: Fix stale return value
    Alexey Kuznetsov found some problems in the pi-futex code.

    The major problem is a stale return value in rt_mutex_slowlock():

    When the pi chain walk returns -EDEADLK, but the waiter was woken up
    during the phases where the locks were dropped, the rtmutex could be
    acquired, but due to the stale return value -EDEADLK returned to the
    caller.

    Reset the return value in the woken up path.

    Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Ingo Molnar <mingo@elte.hu>
    Signed-off-by: Chris Wright <chrisw@sous-sol.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    kernel/rtmutex.c | 11 +++++++++--
    1 files changed, 9 insertions(+), 2 deletions(-)

    diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
    index 4ab17da..9b08847 100644
    --- a/kernel/rtmutex.c
    +++ b/kernel/rtmutex.c
    @@ -659,9 +659,16 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
    * all over without going into schedule to try
    * to get the lock now:
    */
    - if (unlikely(!waiter.task))
    + if (unlikely(!waiter.task)) {
    + /*
    + * Reset the return value. We might
    + * have returned with -EDEADLK and the
    + * owner released the lock while we
    + * were walking the pi chain.
    + */
    + ret = 0;
    continue;
    -
    + }
    if (unlikely(ret))
    break;
    }
    --
    1.5.2.4
    --
    -
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