[patch] softlockup: do the wakeup from a hrtimer

[Ingo Molnar <mingo@elte.hu>]

Subject: softlockup: do the wakeup from a hrtimer
From: Ingo Molnar <mingo@elte.hu>

David Miller reported soft lockup false-positives that trigger on NOHZ 
due to CPUs idling for more than 10 seconds.

The solution is to drive the wakeup of the watchdog threads not from the 
timer tick (which has no guaranteed frequency), but from the watchdog 
tasks themselves.

http://bugzilla.kernel.org/show_bug.cgi?id=9409

Reported-by: David Miller <davem@davemloft.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/softlockup.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

Index: linux/kernel/softlockup.c
===================================================================
--- linux.orig/kernel/softlockup.c
+++ linux/kernel/softlockup.c
@@ -100,10 +100,6 @@ void softlockup_tick(void)
 
 	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 10+ seconds delays: */
 	if (now <= (touch_timestamp + softlockup_thresh))
 		return;
@@ -141,7 +137,7 @@ static int watchdog(void *__bind_cpu)
 	while (!kthread_should_stop()) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		touch_softlockup_watchdog();
-		schedule();
+		msleep(1000);
 	}
 
 	return 0;