Commit 02ff3755 authored May 12, 2008 by Ingo Molnar

softlockup: fix false positives on nohz if CPU is 100% idle for more than 60 seconds



Fix (probably theoretical only) rq->clock update bug:
in tick_nohz_update_jiffies() [which is called on all irq
entry on all cpus where the irq entry hits an idle cpu] we
call touch_softlockup_watchdog() before we update jiffies.
That works fine most of the time when idle timeouts are within
60 seconds. But when an idle timeout is beyond 60 seconds,
jiffies is updated with a jump of more than 60 seconds,
which causes a jump in cpu-clock of more than 60 seconds,
triggering a false positive.

Reported-by: David Miller <davem@davemloft.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 1c4cd6dd

kernel/time/tick-sched.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -133,8 +133,6 @@ void tick_nohz_update_jiffies(void)
		if (!ts->tick_stopped)
		return;

		touch_softlockup_watchdog();

		cpu_clear(cpu, nohz_cpu_mask);
		now = ktime_get();
		ts->idle_waketime = now;
		@@ -142,6 +140,8 @@ void tick_nohz_update_jiffies(void)
		local_irq_save(flags);
		tick_do_update_jiffies64(now);
		local_irq_restore(flags);

		touch_softlockup_watchdog();
		}

		void tick_nohz_stop_idle(int cpu)

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