linux-kernel - Re: perf: fuzzer triggers NULL pointer derefreence in x86_schedule

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Date:	Fri, 8 May 2015 00:25:50 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Stephane Eranian <eranian@...gle.com>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: perf: fuzzer triggers NULL pointer derefreence in
 x86_schedule_events

On Thu, 7 May 2015, Peter Zijlstra wrote:

> Indeed so; and we can make an analogous argument for hwc. However:
> 
> > I think it is more likely related to the bitmask (idxmsk).  But then
> > it is always allocated with the constraint even with the HT bug
> > workaround.  So most, likely the index is bogus and you touch outside
> > the idxmsk[] array.
> 
> [428232.701319] BUG: unable to handle kernel NULL pointer dereference at           (null)
> 
> But the thing really tried to touch NULL, not some random address that
> faulted.
> 
> As always, Vince has found us a good puzzle ;-)

and sorry I haven't been much help tracking it down.  I'm trying to 
trigger it again, but this particular bug only pops up after a week or so 
of fuzzing.  

Vince
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