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

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Message-ID: <20160823084519.GN10153@twins.programming.kicks-ass.net>
Date:   Tue, 23 Aug 2016 10:45:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     Huang Rui <ray.huang@....com>, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: perf: fuzzer crashes immediately on AMD system

On Mon, Aug 22, 2016 at 10:54:32PM -0400, Vince Weaver wrote:
> > > > > 
> > > > > 	perf stat -a -e amd_nb/config=0x37,config1=0x20/ /bin/ls
> > 	amd_uncore_find_online_sibling()
> > function is broken. 
> 
> and that's the problem.  uncore_find_online_sibling() does all kinds of 
> wrong things including sticking active uncore structures in 
> uncore->free_when_cpu_online
> 
> Then uncore_online() comes along and frees those structures.
> 
> Then some other part of the kernel comes and re-uses the free'd data.
> 
> Then when we try to start an event, all of the fields are invalid because 
> the uncore pointer is pointing to re-used data.
> 
> I don't have a patch because I am not 100% clear on what 
> uncore_find_online_sibling() is doing in the first place.

Thanks for doing all that, I'll see if I can make sense of it.