[Intel-gfx] [FIXES 3/3] drm/i915/execlists: Move reset_active() from schedule-out to schedule-in

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-11-11 16:31:09)
> 
> On 11/11/2019 13:32, Chris Wilson wrote:
> > The gem_ctx_persistence/smoketest was detecting an odd coherency issue
> > inside the LRC context image; that the address of the ring buffer did
> > not match our associated struct intel_ring. As we set the address into
> > the context image when we pin the ring buffer into place before the
> > context is active, that leaves the question of where did it get
> > overwritten. Either the HW context save occurred after our pin which
> > would imply that our idle barriers are broken, or we overwrote the
> > context image ourselves. It is only in reset_active() where we dabble
> > inside the context image outside of a serialised path from schedule-out;
> > but we could equally perform the operation inside schedule-in which is
> > then fully serialised with the context pin -- and remains serialised by
> > the engine pulse with kill_context(). (The only downside, aside from
> > doing more work inside the engine->active.lock, was the plan to merge
> > all the reset paths into doing their context scrubbing on schedule-out
> > needs more thought.)
> 
> So process_csb is not under the engine lock and hence schedule_out can 
> race with schedule_in meaning schedule_out should refrain from doing 
> non-trivial work.

I'm stealing that for a comment in schedule_out! Thanks,
-Chris