sched: Make warning less noisy

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20091216170517.807938893@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched.c b/kernel/sched.c
index 8a2bfd3..af7dfa7 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2041,7 +2041,7 @@
 	 * We should never call set_task_cpu() on a blocked task,
 	 * ttwu() will sort out the placement.
 	 */
-	WARN_ON(p->state != TASK_RUNNING && p->state != TASK_WAKING);
+	WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING);
 #endif
 
 	trace_sched_migrate_task(p, new_cpu);