futex: Fix WARN_ON() test for UP

An update of the futex code had a

	WARN_ON(!spin_is_locked(q->lock_ptr))

But on UP, spin_is_locked() is always false, and will
trigger this warning, and even worse, it will exit the function
without doing the necessary work.

Converting this to a WARN_ON_SMP() fixes the problem.
Reported-by: NRichard Weinberger <richard@nod.at>
Tested-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NDarren Hart <dvhart@linux.intel.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <20110317192208.682654502@goodmis.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/futex.c

@@ -782,8 +782,8 @@ static void __unqueue_futex(struct futex_q *q)
 {
 	struct futex_hash_bucket *hb;
 
-	if (WARN_ON(!q->lock_ptr || !spin_is_locked(q->lock_ptr)
-			|| plist_node_empty(&q->list)))
+	if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
+	    || WARN_ON(plist_node_empty(&q->list)))
 		return;
 
 	hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);