[Intel-gfx] [PATCH 18/26] drm/i915: use new iterator in i915_gem_object_last_write_engine

[Tvrtko Ursulin]

On 13/09/2021 14:16, Christian König wrote:
> This is maybe even a fix since the RCU usage here looks incorrect.

What you think is incorrect? Pointless extra rcu locking?

Also, FWIW, I submitted a patch to remove this function altogether since 
its IMO pretty useless, just failed in getting anyone to ack it so far.

Regards,

Tvrtko

> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_object.h | 15 +++++++--------
>   1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index e9eecebf5c9d..3343922af4d6 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -500,16 +500,15 @@ static inline struct intel_engine_cs *
>   i915_gem_object_last_write_engine(struct drm_i915_gem_object *obj)
>   {
>   	struct intel_engine_cs *engine = NULL;
> +	struct dma_resv_cursor cursor;
>   	struct dma_fence *fence;
>   
> -	rcu_read_lock();
> -	fence = dma_resv_get_excl_unlocked(obj->base.resv);
> -	rcu_read_unlock();
> -
> -	if (fence && dma_fence_is_i915(fence) && !dma_fence_is_signaled(fence))
> -		engine = to_request(fence)->engine;
> -	dma_fence_put(fence);
> -
> +	dma_resv_for_each_fence_unlocked(obj->base.resv, &cursor, false,
> +					 fence) {
> +		if (fence && dma_fence_is_i915(fence) &&
> +		    !dma_fence_is_signaled(fence))
> +			engine = to_request(fence)->engine;
> +	}
>   	return engine;
>   }
>   
>