[PATCH 5/6] futex: unlock before returning -EFAULT

[Darren Hart <dvhltc@us.ibm.com>]

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>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Rusty Russell <rusty@rustcorp.com.au>
---

 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);