linux-kernel - Re: perf/tracepoint: another fuzzer generated lockup

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Date:	Fri, 8 Nov 2013 16:15:21 -0500 (EST)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: perf/tracepoint: another fuzzer generated lockup

On Fri, 8 Nov 2013, Frederic Weisbecker wrote:

> On Fri, Nov 08, 2013 at 03:23:07PM -0500, Vince Weaver wrote:
> > On Fri, 8 Nov 2013, Frederic Weisbecker wrote:
> > > 
> > > There seem to be a loop that takes too long in intel_pmu_handle_irq(). Your two
> > > previous reports seemed to suggest that lbr is involved, but not this one.
> > 
> > I may be wrong but I think everything between <NMI> and <EOE> is just
> > noise from the NMI perf-event watchdog timer kicking in.
> 
> Ah good point.
> 
> So the pattern seem to be that irq work/perf_event_wakeup is involved, may be
> interrupting a tracepoint event or so.

I managed to construct a reproducible test case, which is attached.  I 
sometimes have to run it 5-10 times before it triggers.

> It would be nice if you enable CONFIG_FRAME_POINTER in your future reports
> so that we get more precise traces. Or may be you actually enabled it and it
> doesn't work?

No, it's not enabled, I can try setting that in the future.

Vince



View attachment "out.c" of type "TEXT/x-csrc" (2950 bytes)