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Subject: Re: [PATCH v2] [watchdog] combine nmi_watchdog and softlockup
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>, Don Zickus <dzickus@redhat.com>,
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Date: Fri, 16 Apr 2010 16:53:11 +0200
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On Fri, 2010-04-16 at 16:46 +0200, Frederic Weisbecker wrote:
> > > 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. 

Every time you think NMI and spinlock think FAIL.