futex: Use futex_top_waiter() in lookup_pi_state()

No point in open coding the same function again.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: Kees Cook <kees@outflux.net>
Cc: wad@chromium.org
Link: http://lkml.kernel.org/r/20140611204237.092947239@linutronix.deSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/futex.c

@@ -796,21 +796,20 @@ static int
 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
 		union futex_key *key, struct futex_pi_state **ps)
 {
+	struct futex_q *match = futex_top_waiter(hb, key);
 	struct futex_pi_state *pi_state = NULL;
-	struct futex_q *this, *next;
 	struct task_struct *p;
 	pid_t pid = uval & FUTEX_TID_MASK;
 
-	plist_for_each_entry_safe(this, next, &hb->chain, list) {
-		if (match_futex(&this->key, key)) {
+	if (match) {
 		/*
-			 * Sanity check the waiter before increasing
-			 * the refcount and attaching to it.
+		 * Sanity check the waiter before increasing the
+		 * refcount and attaching to it.
 		 */
-			pi_state = this->pi_state;
+		pi_state = match->pi_state;
 		/*
-			 * Userspace might have messed up non-PI and
-			 * PI futexes [3]
+		 * Userspace might have messed up non-PI and PI
+		 * futexes [3]
 		 */
 		if (unlikely(!pi_state))
 			return -EINVAL;
@@ -877,7 +876,6 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
 		*ps = pi_state;
 		return 0;
 	}
-	}
 
 	/*
 	 * We are the first waiter - try to look up the real owner and attach