linux-kernel - Re: [PATCH] perf, x86: catch spurious interrupts after disabling counters

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Date:	Wed, 15 Sep 2010 18:47:51 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Robert Richter <robert.richter@....com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Don Zickus <dzickus@...hat.com>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ying.huang@...el.com" <ying.huang@...el.com>,
	"ming.m.lin@...el.com" <ming.m.lin@...el.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>
Subject: Re: [PATCH] perf, x86: catch spurious interrupts after disabling counters

On Wed, Sep 15, 2010 at 6:46 PM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> On Wed, Sep 15, 2010 at 06:20:34PM +0200, Robert Richter wrote:
>> On 14.09.10 19:41:32, Robert Richter wrote:
>> > I found the reason why we get the unknown nmi. For some reason
>> > cpuc->active_mask in x86_pmu_handle_irq() is zero. Thus, no counters
>> > are handled when we get an nmi. It seems there is somewhere a race
>> > accessing the active_mask. So far I don't have a fix available.
>> > Changing x86_pmu_stop() did not help:
>>
>> The patch below for tip/perf/urgent fixes this.
>>
>> -Robert
>>
>> From 4206a086f5b37efc1b4d94f1d90b55802b299ca0 Mon Sep 17 00:00:00 2001
>> From: Robert Richter <robert.richter@....com>
>> Date: Wed, 15 Sep 2010 16:12:59 +0200
>> Subject: [PATCH] perf, x86: catch spurious interrupts after disabling counters
>>
>> Some cpus still deliver spurious interrupts after disabling a counter.
>> This caused 'undelivered NMI' messages. This patch fixes this.
>>
>> Signed-off-by: Robert Richter <robert.richter@....com>
>> ---
> ...
>
> Hi Robert, thanks a lot for tracking this issue! I might be missing
> something but why don't you clean this ->running mask bits on pmu-stop?
> What if counter gets disabled/freed or whatever before issue any nmis?
> Another question I have still -- is this an hardware issue in general?
>
what's for sure, is that you can have an interrupt in flight by the time
you disable.
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