Re: perf: fuzzer crashes immediately on AMD system

[Peter Zijlstra <peterz@infradead.org>]

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.