linux-kernel - Re: perf/ftrace: fuzzer triggers another warning with PERF_EVENT_IOC_SET

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Date:	Fri, 19 Jun 2015 15:31:09 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Vince Weaver <vincent.weaver@...ne.edu>
cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: perf/ftrace: fuzzer triggers another warning with
 PERF_EVENT_IOC_SET_FILTER

On Fri, 19 Jun 2015, Vince Weaver wrote:
> 
> OK, fuzzing found another test case, this one I can reproduce using perf:

and I'm wrong, I wasn't reproducing it with perf, I was looking at the 
wrong window :(

So weird, definitely I can trigger this warning, but it's not reproducible 
with the fuzzer or with manually trying things.  I'm not really sure how 
that can happen.  

Is it possible that two processes might try to update the preds 
linked-list for an event's filter simultaneously?  So this might be a 
hard-to-trigger race condition?  But I don't think the fuzzer actually 
ever has two threads trying to do ioctl at the same time.  hmmm.

Vince

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