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    Subject[tip:core/futexes] futex: unlock before returning -EFAULT
    Commit-ID:  e8f6386c01a5699c115bdad10271a24076364c97
    Gitweb: http://git.kernel.org/tip/e8f6386c01a5699c115bdad10271a24076364c97
    Author: "Darren Hart" <dvhltc@us.ibm.com>
    AuthorDate: Thu, 12 Mar 2009 00:56:06 -0700
    Commit: Ingo Molnar <mingo@elte.hu>
    CommitDate: Thu, 12 Mar 2009 11:20:57 +0100

    futex: unlock before returning -EFAULT

    Impact: rt-mutex failure case fix

    futex_lock_pi can potentially return -EFAULT with the rt_mutex
    held. This seems like the wrong thing to do as userspace should
    assume -EFAULT means the lock was not taken. Even if it could
    figure this out, we'd be leaving the pi_state->owner in an
    inconsistent state. This patch unlocks the rt_mutex prior to
    returning -EFAULT to userspace.

    Build and boot tested on a 4 way Intel x86_64 workstation.
    Passes basic pthread_mutex and PI tests out of
    ltp/testcases/realtime.

    Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
    Acked-by: Peter Zijlstra <peterz@infradead.org>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    LKML-Reference: <20090312075606.9856.88729.stgit@Aeon>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


    ---
    kernel/futex.c | 7 +++++++
    1 files changed, 7 insertions(+), 0 deletions(-)

    diff --git a/kernel/futex.c b/kernel/futex.c
    index 6579912..c980a55 100644
    --- a/kernel/futex.c
    +++ b/kernel/futex.c
    @@ -1567,6 +1567,13 @@ retry_locked:
    }
    }

    + /*
    + * If fixup_pi_state_owner() faulted and was unable to handle the
    + * fault, unlock it and return the fault to userspace.
    + */
    + if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
    + rt_mutex_unlock(&q.pi_state->pi_mutex);
    +
    /* Unqueue and drop the lock */
    unqueue_me_pi(&q);


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