[Intel-gfx] [PATCH] drm/i915/execlists: Remove incorrect BUG_ON for schedule-out

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-09-09 11:23:56)
> 
> On 07/09/2019 11:50, Chris Wilson wrote:
> > As we may unwind incomplete requests (for preemption) prior to
> > processing the CSB and the schedule-out events, we may update rq->engine
> > (resetting it to point back to the parent virtual engine) prior to
> > calling execlists_schedule_out(), invalidating the assertion that the
> > request still points to the inflight engine. (The likelihood of this is
> > increased if the CSB interrupt processing is pushed to the ksoftirqd for
> > being too slow and direct submission overtakes it.)
> > 
> > Reported-by: Vinay Belgaumkar <vinay.belgaumkar at intel.com>
> > Fixes: df403069029d ("drm/i915/execlists: Lift process_csb() out of the irq-off spinlock")
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > Cc: Vinay Belgaumkar <vinay.belgaumkar at intel.com>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_lrc.c | 1 -
> >   1 file changed, 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > index 3aad35b570d4..16f226349525 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > @@ -631,7 +631,6 @@ execlists_schedule_out(struct i915_request *rq)
> >       struct intel_engine_cs *cur, *old;
> >   
> >       trace_i915_request_out(rq);
> > -     GEM_BUG_ON(intel_context_inflight(ce) != rq->engine);
> >   
> >       old = READ_ONCE(ce->inflight);
> >       do
> > 
> 
> So unwind from direct submission resets rq->engine and races with 
> process_csb from the tasklet which notices request has actually 
> completed?

Yup. That's nice and succinct compared to my waffle.
-Chris