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SubjectRe: [PATCH v2] [watchdog] combine nmi_watchdog and softlockup
On Fri, Apr 16, 2010 at 06:32:32PM +0400, Cyrill Gorcunov wrote:
> On Fri, Apr 16, 2010 at 03:47:14AM +0200, Frederic Weisbecker wrote:
> [...]
> > > +
> > > +/* Callback function for perf event subsystem */
> > > +void watchdog_overflow_callback(struct perf_event *event, int nmi,
> > > + struct perf_sample_data *data,
> > > + struct pt_regs *regs)
> > > +{
> > > + int this_cpu = smp_processor_id();
> > > + unsigned long touch_ts = per_cpu(watchdog_touch_ts, this_cpu);
> > > +
> > > + if (touch_ts == 0) {
> > > + __touch_watchdog();
> > > + return;
> > > + }
> > > +
> > > + /* check for a hardlockup
> > > + * This is done by making sure our timer interrupt
> > > + * is incrementing. The timer interrupt should have
> > > + * fired multiple times before we overflow'd. If it hasn't
> > > + * then this is a good indication the cpu is stuck
> > > + */
> > > + if (is_hardlockup(this_cpu)) {
> > > + /* only print hardlockups once */
> > > + if (cpumask_test_cpu(this_cpu, to_cpumask(hardlockup_mask)))
> > > + return;
> > > +
> > > + if (hardlockup_panic)
> > > + panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
> > > + else
> > > + WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
> > > +
> > > + cpumask_set_cpu(this_cpu, to_cpumask(hardlockup_mask));
> >
> >
> >
> > May be have an arch spin lock there to update your cpu mask safely.
> >
>
> Hmm, this is NMI handler path so from what we protect this per-cpu data?
> Do I miss something? /me confused

It's not per-cpu which is the problem I believe. If you have multiple
cpus dealing with hardlockups than they can overwrite each other's data.

Cheers,
Don


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