linux-kernel - Re: [PATCH v2] [watchdog] combine nmi

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Date:	Fri, 16 Apr 2010 18:54:44 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Don Zickus <dzickus@...hat.com>, mingo@...e.hu,
	peterz@...radead.org, aris@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] [watchdog] combine nmi_watchdog and softlockup

On Fri, Apr 16, 2010 at 04:46:17PM +0200, Frederic Weisbecker wrote:
...
> > > > +		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.
> 

yeah, saw DECLARE_BITMAP but read it as DEFINE_PER_CPU for some reason.
having any spinlock in irq handler is really under suspicious.

	-- Cyrill
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