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Date: Fri, 16 Apr 2010 18:32:32 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Frederic Weisbecker <fweisbec@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
Message-ID: <20100416143232.GA5540@lenovo>
References: <1271366710-17468-1-git-send-email-dzickus@redhat.com> <20100416014712.GC15570@nowhere>
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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

	-- Cyrill