On Fri, 5 Sep 2014, Linus Torvalds wrote:
> However, the more fundamental question is "what protects accesses to
> 'events->ctx'". Why is "put_event()" so special that *it* gets locking
> for the reading of "event->ctx", but none of the other cases of
> reading the ctx pointer gets it or needs it?
>
> I'm getting the feeling that this race is bigger than just put_event().
I've been chasing a bug triggered by my perf_fuzzer program (with a
forking workload) for the past few months. It will reliably oops the
machine or worse (I've had it somehow not only take down the test
machine, but the whole local network somehow).
Often it seems to come from deep inside the perf_event context locking, in
conjunction with complex open/fork/close/migrate workloads.
Here's a link to an older bug writeup, I've had it happen more recently
but I've been too busy to bother writing it up.
http://web.eece.maine.edu/~vweaver/projects/perf_events/fuzzer/3.15-rc5.get_cpu_context_gpf.html
Is there hope that we've finally found a plausible source for this bug?
Vince
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