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>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 6579912ee70c..c980a556f82c 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);