[PATCH] hardlockup: detect hard lockups without NMIs using secondary cpus

[tony@atomide.com (Tony Lindgren)]

* Colin Cross <ccross@android.com> [130110 14:37]:
> 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.

OK thanks for clarifying that.

Tony