linux-kernel - Re: [perf] more perf_fuzzer memory corruption

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Date:	Thu, 17 Apr 2014 11:35:45 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [perf] more perf_fuzzer memory corruption

On Thu, 17 Apr 2014, Peter Zijlstra wrote:
> 
> Meh.. my machine keeps locking up with 15-rc1 and your fuzzer. It looks
> to get stuck a finish_task_switch() from a preemption while waiting for
> a perf IPI.
> 
> Which is complete crack because we have preemption disabled over
> issueing and waiting for the IPI :/
> 
> I tried reverting some of the IPI related patches, but no joy so far,
> I'm about to go try a git-bisect on this.

Bisecting can be a pain, as if you go too far back you start running into 
other bugs that have been fixed due to the fuzzer.

Over the past year there's been at least 10 perf_fuzzer-related crash 
fixes that have gotten into the kernel.  It used to be I could crash 
things in seconds, it's now up to minutes-hours but the bugs are that much 
harder to isolate :(

And I still am not fuzzing with signal-overflow enabled, which 
causes even more pain.

Vince
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