linux-kernel - Re: perf: perf_fuzzer triggers instant reboot

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Date:	Wed, 10 Sep 2014 09:18:35 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: perf: perf_fuzzer triggers instant reboot

On Wed, 10 Sep 2014, Peter Zijlstra wrote:
> 
> Sasha reported something from his KVM based fuzzing, maybe that's the
> same. But that x86_exceptions thing is interesting, lemme go look at
> that first.

that's what got me looking at things again, the trinity reports.  Though I 
think those involve CPU hotplugging which my fuzzer shouldn't trigger.

I do think this is the same memory corruption/reboot bug that I reported 
back in February (the thread is "perf_fuzzer compiled for x32 causes 
reboot" but I wasn't able to isolate the problem then either.

Somehow something is stomping over memory with a forking workload (likely 
an improper free with RCU like we've seen before) but the fact that it 
causes a reboot immediately makes it *really* hard to debug this.

I'm not sure about the tracing issue, possibly it's just a side effect of 
memory being corrupted by the same bug.  In case it's relevant here's the 
trace-cmd I was trying to use:

   trace-cmd record -e raw_syscalls -p function -l '*perf*' -n 'perf_event_task_tick' -l 'x86*' -l 'intel*' -P 2807

Vince
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