Re: perf: perf_fuzzer lockup in perf_cgroup_attach

Vince Weaver
2016-09-15T12:41:57Z

On Thu, 15 Sep 2016, Peter Zijlstra wrote:

> On Wed, Sep 14, 2016 at 10:43:29PM -0400, Vince Weaver wrote:
> >
> > so the skylake that was fuzzing finally is mostly locked up.
> >
> > Really hard to tell what's going, especially as KASLR made looking up the
> > addresses a big pain.
> >
> > The best I can tell things are getting wedged somehow in
> > perf_cgroup_switch() while interrupts are disabled. Interrupts are never
> > getting re-enabled, causing the RCU and NMI watchdogs to trigger (and more
> > alarming things like the SATA bus resetting).
>
> How do you go about using cgroups? Do you set them up yourself, does the
> fuzzer do so?

that's an interesting thing, I don't think the fuzzer actually sets up any
cgroups. It will try creating events with PERF_FLAG_PID_CGROUP but it
will just use a random number as the cgroup fd.

I know at one time I meant to do more interesting things with cgroups
but if I recall it wasn't really possible without running as root and I
usually don't fuzz as root.

Vince