[Intel-gfx] [PATCH] drm/i915: Return early for await_start on same timeline

[Tvrtko Ursulin]

On 05/03/2020 13:48, Chris Wilson wrote:
> Requests within a timeline are ordered by that timeline, so awaiting for
> the start of a request within the timeline is a no-op. This used to work
> by falling out of the mutex_trylock() as the signaler and waiter had the
> same timeline and not returning an error.
> 
> Fixes: 6a79d848403d ("drm/i915: Lock signaler timeline while navigating")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> Cc: <stable at vger.kernel.org> # v5.5+
> ---
>   drivers/gpu/drm/i915/i915_request.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 46dae33c1a20..ca5361eb1f0b 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -837,8 +837,8 @@ i915_request_await_start(struct i915_request *rq, struct i915_request *signal)
>   	struct dma_fence *fence;
>   	int err;
>   
> -	GEM_BUG_ON(i915_request_timeline(rq) ==
> -		   rcu_access_pointer(signal->timeline));
> +	if (i915_request_timeline(rq) == rcu_access_pointer(signal->timeline))
> +		return 0;
>   
>   	if (i915_request_started(signal))
>   		return 0;
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Regards,

Tvrtko