On Tue, 23 Aug 2016, Peter Zijlstra wrote: > 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.
I should have provided more detail, was just tired after chasing the bug for so long. I mostly found things by sprinkling printks everywhere. Comenting out the call to kfree() in uncore_online() makes the code stop crashing (but perhaps causes a memory leak?) In any case it's odd the problem didn't show up earlier, but maybe the recent changes to CPU hotplugging in that file exposed the issue. Vince
