v3.13-rc6+ regression (ARM board)

[Linus Torvalds]

On Thu, Jan 2, 2014 at 12:30 PM, John Stultz <john.stultz at linaro.org> wrote:
>
> So something else may be at play. Even with Linus' patch I reproduced a
> similar hang here.
>
> Still chasing it down, but it looks like a seqlock deadlock where we're
> calling read while holding the lock.

Hmm. Only with lockdep, right?

Does lockdep perhaps read the scheduler clock? Afaik, we have
lockstat_clock(), which uses local_clock(), which in turn translates
to sched_clock_cpu(smp_processor_id())..

So if that code now tries to read the scheduler clock when
update_sched_clock() is doing a update and has done a
write_seqcount_begin()...

    Linus