linux-kernel - Re: [PATCH -tip] perf, x86: fix unknown NMIs on a Pentium4 box

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Date:	Thu, 14 Apr 2011 15:57:48 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Lin Ming <ming.m.lin@...el.com>,
	Shaun Ruffell <sruffell@...ium.com>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...gle.com>,
	Robert Richter <robert.richter@....com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] perf, x86: fix unknown NMIs on a Pentium4 box

On Thu, Apr 14, 2011 at 11:43:25PM +0400, Cyrill Gorcunov wrote:
> On 04/14/2011 10:46 PM, Ingo Molnar wrote:
> > 
> > btw., the bug went away once i removed your patch so it's 100% sure caused by 
> > this change.
> > 
> > Thanks,
> > 
> > 	Ingo
> 
> Ingo if you have a chance mind to give this patch a shot please? Seems we might miss unmasking
> for inflight nmis.

I don't think this patch will work.  It would make sense if the unmasking
happened _after_ the "if (!handled)" path, but that is not the path Ingo
wanted for v1.

Cheers,
Don

> -	apic_write(APIC_LVTPC, APIC_DM_NMI);
> 
>  	handled = x86_pmu.handle_irq(args->regs);
> +	apic_write(APIC_LVTPC, APIC_DM_NMI);

^^^^ all handled/unhandled NMIs hit that apic_write
>  	if (!handled)
>  		return NOTIFY_DONE;
> 
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