linux-kernel - Re: perf: perf_fuzzer crashes on Pentium 4 systems

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Date:   Thu, 4 Apr 2019 19:47:00 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...hat.com>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: perf: perf_fuzzer crashes on Pentium 4 systems

On Thu, Apr 04, 2019 at 12:37:18PM -0400, Vince Weaver wrote:
> On Thu, 4 Apr 2019, Cyrill Gorcunov wrote:
> 
> > On Thu, Apr 04, 2019 at 09:25:47AM -0400, Vince Weaver wrote:
> > > 
> > > It looks like there are at least two bugs here, one that's a full 
> > > hardlockup with nothing on serial console.  The other is the NULL 
> > > dereference.
> 
> OK, it turns out the hard-lock and the null pointer dereference might be 
> the same, I have a random seed for the fuzzer from a hard-lock crash that 
> reproduces and it generated the null pointer crash.  (This is with your 
> patch applied).

I see. My patch simply eliminates wrong event for unimplemented general
events, but it definitely won't help with nil deref, so it mostly to
eliminate some potential side effects.

> I can try to see if I can bisect down to a specific event sequence that 
> triggers this, but that can be tricky sometimes if things lock up so fast 
> that the event log doesn't get written out before the crash.

Oh, Vince, I suspect such kind of bisection might consume a lot of your
time :( Maybe we could update perf fuzzer so that it would send events
to some net-storage first then write them to the counters, iow to automatize
this all stuff somehow?