futex_unlock_pi() hurts my brain and may cause application deadlock

Avoid futex_unlock_pi returning -EFAULT (which results in deadlock), by
clearing uval before jumping to retry_locked.
Signed-off-by: NJohn Stultz <johnstul@us.ibm.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/futex.c

@@ -1670,6 +1670,7 @@ static int futex_unlock_pi(u32 __user *uaddr, struct rw_semaphore *fshared)
 					 attempt);
 		if (ret)
 			goto out;
+		uval = 0;
 		goto retry_unlocked;
 	}