[Intel-gfx] [PATCH] drm/i915: Cancel pending execlist tasklet upon wedging

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-06-21 14:33:59)
> 
> On 21/06/2017 13:48, Chris Wilson wrote:
> > Highly unlikely, but if the stop_machine() did suspend the tasklet, we
> > want to make sure that when it wakes it finds there is nothing to do.
> > Otherwise, it will loudly complain that the ELSP port tracking no longer
> > matches the hardware, and we will be mightly confused.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_gem.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 1353491c1010..ae3ce1314bd1 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -3092,6 +3092,13 @@ static void engine_set_wedged(struct intel_engine_cs *engine)
> >               engine->execlist_first = NULL;
> >   
> >               spin_unlock_irqrestore(&engine->timeline->lock, flags);
> > +
> > +             /* The port is checked prior to scheduling a tasklet, but
> > +              * just in case we have suspended the tasklet to do the
> > +              * wedging make sure that when it wakes, it decides there
> > +              * is no work to do by clearing the irq_posted bit.
> > +              */
> > +             clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
> >       }
> >   }
> >   
> > 
> 
> Or tasklet_kill? Actually I am not sure now how the wedging transition 
> works for request which have pasted the submit callback, but are not in 
> the hardware yet (waiting in the priotree). Can't find at the moment 
> that we have anything dealing with those.

We kill the rbtree and the tree itself doesn't hold a reference to the
request (just a reference is held for the ports, as prior to submission
there is no way we complete the request and so cancel the in-flight
reference count). That's the

	engine->execlist_queue = RB_ROOT;
	engine->execlist_first = NULL;

above.
-Chris