linux-kernel - Re: perf_fuzzer crash on pentium 4

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Date:	Fri, 9 May 2014 20:30:38 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	Don Zickus <dzickus@...hat.com>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: perf_fuzzer crash on pentium 4

On Fri, May 09, 2014 at 12:19:49PM -0400, Vince Weaver wrote:
> On Thu, 8 May 2014, Cyrill Gorcunov wrote:
> > 
> > Updated.
> > ---
> >  arch/x86/kernel/cpu/perf_event_p4.c |   67 ++++++++++++++++--------------------
> >  1 file changed, 30 insertions(+), 37 deletions(-)
> 
> I tried this patch, and even though it seemed to fix one of the NMI storms 
> I was experiencing I've managed to trigger again using a different random 
> seed.

Thanks a lot for help in testing, Vince! I think the patch would be still
needed so I will prepare normal change log explaining what has been fixed
in the patch.

> I've been trying to track down a trace of what is triggering things, but 
> this is very difficult as the full log isn't making it to the serial 
> console, even when I fsync() stdout.

I see. Need to think. Maybe something comes to mind. Debuggin it is really
a hard job :/ I've been promised to get access to real p4 machine next
week, maybe I find something.

> Maybe related, but the following messages tend to happen a lot while 
> fuzzing, and always happen before the fuzzing that eventually locks up:
> 
> The warnings are for
> 	if (WARN_ON_ONCE(!(event->hw.state & PERF_HES_STOPPED)))
> and
> 	WARN_ON_ONCE(hwc->state & PERF_HES_STOPPED);	

Thanks for info, Vince! Look, every time you start perf_fuzzer (note,
I didn't read its code yet, that's why I'm asking) -- does it log
which events are passed to kernel from userspace? Btw, do you run
kernel with nmi-watchdog turned on?
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