From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>, mingo@kernel.org,
        eranian@google.com
Cc: linux-kernel@vger.kernel.org, vince@deater.net, dvyukov@google.com,
        andi@firstfloor.org, jolsa@redhat.com, panand@redhat.com,
        sasha.levin@oracle.com, oleg@redhat.com,
        Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 00/12] perf: more fixes
In-Reply-To: <20160310143924.GR6356@twins.programming.kicks-ass.net>
References: <20160224174539.570749654@infradead.org> <20160310143924.GR6356@twins.programming.kicks-ass.net>
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Date: Fri, 11 Mar 2016 12:12:56 +0200
Message-ID: <87r3fh8grb.fsf@ashishki-desk.ger.corp.intel.com>
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Peter Zijlstra <peterz@infradead.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@infradead.org>

FWIW,

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

Cheers,
--
Alex