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SubjectRe: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule
On Mon, 13 May 2013, Thomas Gleixner 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))

The warning is gone, so it definitely looks like you found a culprit,
Thomas, thanks.

But I am not going to provide my Tested-by: yet, as one of the four
suspend-resume cycles I have done during testing of this patch ended up
with segfaults when trying to start any userspace binary after resume
(i.e. clear memory corruption). The remaining three suspend-resume
cycles were fine.

Will be looking into this a little bit more.

--
Jiri Kosina
SUSE Labs


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