linux-kernel - Re: [PATCH 00/12] perf: more fixes

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Date:	Fri, 11 Mar 2016 12:12:56 +0200
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	eranian@...gle.com
Cc:	linux-kernel@...r.kernel.org, vince@...ter.net, dvyukov@...gle.com,
	andi@...stfloor.org, jolsa@...hat.com, panand@...hat.com,
	sasha.levin@...cle.com, oleg@...hat.com,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 00/12] perf: more fixes

Peter Zijlstra <peterz@...radead.org> writes:

> On Wed, Feb 24, 2016 at 06:45:39PM +0100, Peter Zijlstra wrote:
>
>> With these patches syz-kaller can still trigger some fail; most notably some
>> NMI watchdog triggers and a very sporadic unthrottle bug (much like last time).
>
> So the below seems to make the sporadic unthrottle thing much less
> likely in that I haven't seen it in several hours, my machine keeps
> dying on NMI watchdog bits.
>
> Boris, who has been running syz-kaller on AMD hardware and was hitting a
> very similar bug with the AMD-IBS code, says its not fixed it for him,
> so maybe there's still more to find.
>
> ---
> Subject: perf: Fix unthrottle
>
> Its possible to IOC_PERIOD while the event is throttled, this would
> re-start the event and the next tick would then try to unthrottle it,
> and find the event wasn't actually stopped anymore.
>
> This would tickle a WARN in the x86-pmu code which isn't expecting to
> start a !stopped event.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

FWIW,

Reviewed-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>

Cheers,
--
Alex