tracing: Robustify wait loop

The pending nested sleep debugging triggered on the potential stale
TASK_INTERRUPTIBLE in this code.

While there, fix the loop such that we won't revert to a while(1)
yield() 'spin' loop if we ever get a spurious wakeup.

And fix the actual issue by properly terminating the 'wait' loop by
setting TASK_RUNNING.

Link: http://lkml.kernel.org/p/20141008165110.GA14547@worktop.programming.kicks-ass.net

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_events.c

@@ -2513,8 +2513,11 @@ static __init int event_test_thread(void *unused)
 	kfree(test_malloc);
 
 	set_current_state(TASK_INTERRUPTIBLE);
-	while (!kthread_should_stop())
+	while (!kthread_should_stop()) {
 		schedule();
+		set_current_state(TASK_INTERRUPTIBLE);
+	}
+	__set_current_state(TASK_RUNNING);
 
 	return 0;
 }