Re: perf: perf_fuzzer crashes on Pentium 4 systems

[Cyrill Gorcunov <gorcunov@gmail.com>]

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?