[Intel-gfx] [drm-intel-nightly] 2016y-07m-14d-21h-13m-02s UTC: locking dependency: drm_modeset_lock_all() || __blocking_notifier_call_chain

[Johannes Berg]

On Wed, 2016-08-17 at 19:27 +0000, Sedat Dilek wrote:
> 
> > > The call-trace is reproducible with my setup and seen on every
> > > boot.

Might have been nice to keep the backtrace when adding new people :)

I found it here:
https://lists.freedesktop.org/archives/intel-gfx/2016-July/100695.html

> [ CC Peter, Johannes and Thorsten "The regression reporter" ]
> 
> Peter has 2 fixes from Johannes in peterz/queue.git#locking/urgent
> which fix the issue for me.
> 
> [1/2] Revert "drm/fb-helper: Reduce READ_ONCE(master) to
> lockless_dereference"
> [2/2] locking/barriers: suppress sparse warnings in
> lockless_dereference()

I don't see how those could fix it. The second one is a pure compile-
time issue, so it's completely irrelevant - it should not change code
generation in any way.

The first one, reverting to READ_ONCE(), does change the code a bit,
but since lockless_dereference() has no lockdep involvement, I don't
see how that could have any impact on a lockdep report.

Judging from the lockdep report, you have a pretty simple ABBA deadlock
there, but I really don't see how the changes could have any impact.

johannes