softlockup: fix task state setting

kthread_stop() can be called when a 'watchdog' thread is executing after
kthread_should_stop() but before set_task_state(TASK_INTERRUPTIBLE).
Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/softlockup.c

@@ -216,26 +216,27 @@ static int watchdog(void *__bind_cpu)
 	/* initialize timestamp */
 	touch_softlockup_watchdog();
 
+	set_current_state(TASK_INTERRUPTIBLE);
 	/*
 	 * Run briefly once per second to reset the softlockup timestamp.
 	 * If this gets delayed for more than 60 seconds then the
 	 * debug-printout triggers in softlockup_tick().
 	 */
 	while (!kthread_should_stop()) {
-		set_current_state(TASK_INTERRUPTIBLE);
 		touch_softlockup_watchdog();
 		schedule();
 
 		if (kthread_should_stop())
 			break;
 
-		if (this_cpu != check_cpu)
-			continue;
-
-		if (sysctl_hung_task_timeout_secs)
-			check_hung_uninterruptible_tasks(this_cpu);
+		if (this_cpu == check_cpu) {
+			if (sysctl_hung_task_timeout_secs)
+				check_hung_uninterruptible_tasks(this_cpu);
+		}
 
+		set_current_state(TASK_INTERRUPTIBLE);
 	}
+	__set_current_state(TASK_RUNNING);
 
 	return 0;
 }