linux-kernel - Re: perf: fuzzer crashes immediately on AMD system

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Message-ID: <alpine.DEB.2.20.1608191100350.24564@macbook-air>
Date:   Fri, 19 Aug 2016 11:03:23 -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, Borislav Petkov <bp@...e.de>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Huang Rui <ray.huang@....com>
Subject: Re: perf: fuzzer crashes immediately on AMD system

On Fri, 19 Aug 2016, Peter Zijlstra wrote:

> On Thu, Aug 18, 2016 at 10:46:31AM -0400, Vince Weaver wrote:
> > On Thu, 18 Aug 2016, Vince Weaver wrote:
> > 
> > > Tried the perf_fuzzer on my A10 fam15h/model13h system with 4.8-rc2 and it
> > > falls over more or less immediately.
> > > 
> > > This maps to variable_test_bit()
> > > 	called by ctx = find_get_context(pmu, task, event);
> > > 		in kernel/events/core.c:9467
> > > 
> > > It happens quickly enough I can probably track down the exact event that 
> > > causes this, if needed.
> > 
> > I have a one line reproducer:
> > 
> > 	perf stat -a -e amd_nb/config=0x37,config1=0x20/ /bin/ls
> 
> OK, cannot reproduce on my fam15h/model1h. I'll go dig through the
> various manuals to see if I can spot the fail.
> 
> Huang could you either prod someone at AMD or do yourself, audit the AMD
> perf code for all the various new models?


OK, this is weird.  I rebooted (didn't patch the kernel, just rebooted) 
and I can't reproduce the original problem at all.

It was perfectly repeatable before I rebooted, dumped an OOPS message 
every time.

Sadly I don't have the fuzzer logs that originally triggered the bug (need 
more serial/USB cables.  Actually no, I need more null-modem adapters).

Let me look into this a bit more.

Vince