linux-kernel - Re: perf: 3.17 another perf

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Message-ID: <alpine.DEB.2.11.1410200045530.19577@vincent-weaver-1.umelst.maine.edu>
Date:	Mon, 20 Oct 2014 00:48:43 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Vince Weaver <vincent.weaver@...ne.edu>
cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: perf: 3.17 another perf_fuzzer lockup

On Fri, 17 Oct 2014, Vince Weaver wrote:

> On Fri, 17 Oct 2014, Vince Weaver wrote:
> 
> > Now to find out why this could happen.  Probably something to do with 
> > crazy RCU magic :(
> 
> it looks like there's an unbalanced get_ctx() / put_ctx() here, as the
> software event context on the main process should not get decremented
> to 0 unless that process is exiting, yet it happens.
> 
> Maybe this is bisectable.  Hmmm.

nope.  Wasted 3 days trying to bisect this.  Something during the 3.17 
merge window changed enough to make the perf_fuzzer results 
non-deterministic, and that makes it nearly impossibe to reproduce the
issue properly.  Ugh.  I might be reduced to sprinkling printks around 
unless anyone chimes in with better advice.

Vince
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