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

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Message-ID: <20131108204839.GD14606@localhost.localdomain>
Date:	Fri, 8 Nov 2013 21:48:41 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	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, 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.

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?
 
> Why that code would be reading the LBR registers I don't know.

Yeah that's just an inconditional call to check if there is lbr branch to record.

> Vince
> 
> 
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