Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123native_smp_send_reschedule

[Thomas Gleixner]

On Mon, 13 May 2013, Jiri Kosina wrote:
> > --- a/kernel/time/tick-sched.c
> > +++ b/kernel/time/tick-sched.c
> > @@ -650,6 +650,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
> >  
> >  			ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
> >  			ts->tick_stopped = 1;
> > +			WARN_ON_ONCE(!cpu_online(cpu));

So that warning triggers.

>  WARNING: at kernel/time/tick-sched.c:653 tick_nohz_stop_sched_tick+0x38e/0x3a0()

The pre full dyntick idle code bailed out when a cpu was offline. The
new fangled can_stop_idle_tick() function dropped that.

Does the patch below fix the issue?

Thanks,

	tglx

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index bc67d42..00a9a97 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -717,6 +717,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 	if (unlikely(!cpu_online(cpu))) {
 		if (cpu == tick_do_timer_cpu)
 			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
+		return false;
 	}
 
 	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))

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