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SubjectRe: [PATCH] hardlockup: detect hard lockups without NMIs using secondary cpus
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On Thu, Jan 10, 2013 at 12:38 PM, Tony Lindgren <tony@atomide.com> wrote:
>
> * Colin Cross <ccross@android.com> [130109 18:05]:
> > +static void watchdog_check_hardlockup_other_cpu(void)
> > +{
> > + int cpu;
> > + cpumask_t cpus = watchdog_cpus;
> > +
> > + /*
> > + * Test for hardlockups every 3 samples. The sample period is
> > + * watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over
> > + * watchdog_thresh (over by 20%).
> > + */
> > + if (__this_cpu_read(hrtimer_interrupts) % 3 != 0)
> > + return;
> > +
> > + /* check for a hardlockup on the next cpu */
> > + cpu = cpumask_next(smp_processor_id(), &cpus);
>
> Hmm don't you want to check cpu_oneline_mask here and
> return if the other CPU is offline?

watchdog_cpus is effectively a local copy of cpu_online_mask, but
updated after the watchdog_nmi_touch in watchdog_nmi_enable. This
avoids a false positive after hotplugging in a cpu when
cpu_online_mask is true but that cpu hasn't yet run it's first
hrtimer.

> > + if (cpu >= nr_cpu_ids)
> > + cpu = cpumask_first(&cpus);
> > + if (cpu == smp_processor_id())
> > + return;
>
> Regards,
>
> Tony


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