[Intel-gfx] [PATCH 04/27] drm/i915/guc: Don't drop ce->guc_active.lock when unwinding context

[Matthew Brost]

On Thu, Aug 19, 2021 at 05:01:03PM -0700, Daniele Ceraolo Spurio wrote:
> 
> 
> On 8/18/2021 11:16 PM, Matthew Brost wrote:
> > Don't drop ce->guc_active.lock when unwinding a context after reset.
> > At one point we had to drop this because of a lock inversion but that is
> > no longer the case. It is much safer to hold the lock so let's do that.
> > 
> > Fixes: eb5e7da736f3 ("drm/i915/guc: Reset implementation for new GuC interface")
> > Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> > Cc: <stable at vger.kernel.org>
> 
> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> 
> Do we have a trybot of this series with GuC enabled? I've checked the
> functions called in the previously unlocked chunk and didn't spot anything
> requiring the lock to be dropped, but I'd feel safer if we had lockdep
> results as well.
> 

RKL uses GuC submission with BAT. This has been thoroughly tested by me
too and no lockdep splats. Can kick off a trybot on the next rev of this
series too.

Matt

> Daniele
> 
> > ---
> >   drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 4 ----
> >   1 file changed, 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > index 9ca0ba4ea85a..e4a099f8f820 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -812,8 +812,6 @@ __unwind_incomplete_requests(struct intel_context *ce)
> >   			continue;
> >   		list_del_init(&rq->sched.link);
> > -		spin_unlock(&ce->guc_active.lock);
> > -
> >   		__i915_request_unsubmit(rq);
> >   		/* Push the request back into the queue for later resubmission. */
> > @@ -826,8 +824,6 @@ __unwind_incomplete_requests(struct intel_context *ce)
> >   		list_add(&rq->sched.link, pl);
> >   		set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
> > -
> > -		spin_lock(&ce->guc_active.lock);
> >   	}
> >   	spin_unlock(&ce->guc_active.lock);
> >   	spin_unlock_irqrestore(&sched_engine->lock, flags);
>