[PATCH 13/27] drm/i915/guc: Take context ref when cancelling request

[Matthew Brost]

On Fri, Aug 20, 2021 at 05:07:27PM -0700, Daniele Ceraolo Spurio wrote:
> 
> 
> On 8/18/2021 11:16 PM, Matthew Brost wrote:
> > A context can get destroyed after cancelling a request so take a
> > reference to context when cancelling a request.
> 
> What's the exact race? AFAICS __i915_request_skip does not have a
> context_put().

This commit message isn't quite right, it is really a context reset or a
GT reset which could result in the context getting destroyed. I haven't
actually seen this happen but this just being paranoid about ref
counting. Can fix up the commit message.

Matt

> 
> Daniele
> 
> > 
> > Fixes: 62eaf0ae217d ("drm/i915/guc: Support request cancellation")
> > Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> > ---
> >   drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > 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 e0e85e4ad512..85f96d325048 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -1620,8 +1620,10 @@ static void guc_context_cancel_request(struct intel_context *ce,
> >   				       struct i915_request *rq)
> >   {
> >   	if (i915_sw_fence_signaled(&rq->submit)) {
> > -		struct i915_sw_fence *fence = guc_context_block(ce);
> > +		struct i915_sw_fence *fence;
> > +		intel_context_get(ce);
> > +		fence = guc_context_block(ce);
> >   		i915_sw_fence_wait(fence);
> >   		if (!i915_request_completed(rq)) {
> >   			__i915_request_skip(rq);
> > @@ -1636,6 +1638,7 @@ static void guc_context_cancel_request(struct intel_context *ce,
> >   		flush_work(&ce_to_guc(ce)->ct.requests.worker);
> >   		guc_context_unblock(ce);
> > +		intel_context_put(ce);
> >   	}
> >   }
>