debug: softlockup looping fix

Rafael J. Wysocki reported weird, multi-seconds delays during
suspend/resume and bisected it back to:

commit 82a1fcb90287052aabfa235e7ffc693ea003fe69
Author: Ingo Molnar <[e-mail]>
Date: Fri Jan 25 21:08:02 2008 +0100

softlockup: automatically detect hung TASK_UNINTERRUPTIBLE tasks

fix it:

- restore the old wakeup mechanism
- fix break usage in do_each_thread() { } while_each_thread().
- fix the hotplug switch stmt, a fall-through case was broken.

Bisected-by: Rafael J. Wysocki <[e-mail]>
Signed-off-by: Peter Zijlstra <[e-mail]>
Tested-by: Rafael J. Wysocki <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Acked-by: Rafael J. Wysocki <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/softlockup.c

···
 
 	now = get_timestamp(this_cpu);
 
+	/* Wake up the high-prio watchdog task every second: */
+	if (now > (touch_timestamp + 1))
+		wake_up_process(per_cpu(watchdog_task, this_cpu));
+
 	/* Warn about unreasonable delays: */
 	if (now <= (touch_timestamp + softlockup_thresh))
 		return;
···
 	read_lock(&tasklist_lock);
 	do_each_thread(g, t) {
 		if (!--max_count)
-			break;
+			goto unlock;
 		if (t->state & TASK_UNINTERRUPTIBLE)
 			check_hung_task(t, now);
 	} while_each_thread(g, t);
-
+ unlock:
 	read_unlock(&tasklist_lock);
 }
 
···
 	 * debug-printout triggers in softlockup_tick().
 	 */
 	while (!kthread_should_stop()) {
+		set_current_state(TASK_INTERRUPTIBLE);
 		touch_softlockup_watchdog();
-		msleep_interruptible(10000);
+		schedule();
+
+		if (kthread_should_stop())
+			break;
 
 		if (this_cpu != check_cpu)
 			continue;
 
 		if (sysctl_hung_task_timeout_secs)
 			check_hung_uninterruptible_tasks(this_cpu);
+
 	}
 
 	return 0;
···
 		wake_up_process(per_cpu(watchdog_task, hotcpu));
 		break;
 #ifdef CONFIG_HOTPLUG_CPU
-	case CPU_UP_CANCELED:
-	case CPU_UP_CANCELED_FROZEN:
-		if (!per_cpu(watchdog_task, hotcpu))
-			break;
-		/* Unbind so it can run.  Fall thru. */
-		kthread_bind(per_cpu(watchdog_task, hotcpu),
-			     any_online_cpu(cpu_online_map));
 	case CPU_DOWN_PREPARE:
 	case CPU_DOWN_PREPARE_FROZEN:
 		if (hotcpu == check_cpu) {
···
 			check_cpu = any_online_cpu(temp_cpu_online_map);
 		}
 		break;
+
+	case CPU_UP_CANCELED:
+	case CPU_UP_CANCELED_FROZEN:
+		if (!per_cpu(watchdog_task, hotcpu))
+			break;
+		/* Unbind so it can run.  Fall thru. */
+		kthread_bind(per_cpu(watchdog_task, hotcpu),
+			     any_online_cpu(cpu_online_map));
 	case CPU_DEAD:
 	case CPU_DEAD_FROZEN:
 		p = per_cpu(watchdog_task, hotcpu);