From: Frederic Weisbecker <fweisbec@gmail.com>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>,
mingo@elte.hu, peterz@infradead.org, aris@redhat.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] [watchdog] combine nmi_watchdog and softlockup
Date: Fri, 16 Apr 2010 16:46:17 +0200 [thread overview]
Message-ID: <20100416144616.GC5162@nowhere> (raw)
In-Reply-To: <20100416143232.GA5540@lenovo>
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
The cpu mask is not per cpu here, this is a shared bitmap, so you
can race against other cpus NMIs.
That said, as I suggested, having a per cpu var that we set when we
warned would be much better than a spinlock here.
next prev parent reply other threads:[~2010-04-16 14:46 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-15 21:25 [PATCH v2] [watchdog] combine nmi_watchdog and softlockup Don Zickus
2010-04-15 22:32 ` Randy Dunlap
2010-04-16 14:12 ` Don Zickus
2010-04-16 1:47 ` Frederic Weisbecker
2010-04-16 14:12 ` Don Zickus
2010-04-16 14:43 ` Frederic Weisbecker
2010-04-16 15:04 ` Don Zickus
2010-04-16 15:32 ` Frederic Weisbecker
2010-04-16 16:14 ` Don Zickus
2010-04-16 16:24 ` Frederic Weisbecker
2010-04-16 14:32 ` Cyrill Gorcunov
2010-04-16 14:46 ` Frederic Weisbecker [this message]
2010-04-16 14:53 ` Peter Zijlstra
2010-04-16 14:59 ` Frederic Weisbecker
2010-04-16 14:54 ` Cyrill Gorcunov
2010-04-16 14:46 ` Don Zickus
2010-04-19 21:21 ` Don Zickus
2010-04-19 21:35 ` Ingo Molnar
2010-04-19 21:51 ` Don Zickus
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