[Intel-gfx] [PATCH] drm/i915/psr: Chase psr.enabled only under the psr.lock

[Chris Wilson]

Quoting Rodrigo Vivi (2018-04-06 23:18:16)
> On Fri, Apr 06, 2018 at 11:12:27AM -0700, Souza, Jose wrote:
> > On Thu, 2018-04-05 at 12:49 +0100, Chris Wilson wrote:
> > > +           struct drm_crtc *crtc =
> > > +                   dp_to_dig_port(intel_dp)->base.base.crtc;
> 
> I'm afraid that the issue is this pointer here. So this will only mask
> the issue.
> 
> Should we maybe stash the pipe? :/

It's not that bad. pipe cannot change until after psr_disable is called,
right? And psr_disable ensures that this worker is flushed. The current
problem is just the coordination of cancelling the worker, where we may
set psr.enabled to NULL right before the worker grabs it and
dereferences it.

So if we lock until we have the pipe, we know that dereference chain is
valid, and we know that psr_disable() cannot complete until we complete
the wait. So the pipe remains valid until we return (so long as the pipe
exists when we start).
-Chris