Re: [PATCH] drm/i915: Check the target has not already completed before waiting on it

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 03/05/2019 14:52, Chris Wilson wrote:
> When we want to wait for a request to be executed, we first ask if it is
> not on the GPU  as if it's on the gpu, there's no need to wait. However,
> we have to take into account that a request may not be on the GPU
> because it has already completed!
> 
> The window is small due to the numerous preceding checks that our target
> has not yet completed, yet there is still a very small window across the
> kmalloc.
> 
> Fixes: e88619646971 ("drm/i915: Use HW semaphores for inter-engine synchronisation on gen8+")
> Testcase: igt/gem_concurrent_blit
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_request.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index d06c45305b03..6dbf8dc5cd6a 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -373,7 +373,7 @@ i915_request_await_execution(struct i915_request *rq,
>   	init_irq_work(&cb->work, irq_execute_cb);
>   
>   	spin_lock_irq(&signal->lock);
> -	if (i915_request_is_active(signal)) {
> +	if (i915_request_is_active(signal) || i915_request_completed(signal)) {
>   		i915_sw_fence_complete(cb->fence);
>   		kmem_cache_free(global.slab_execute_cbs, cb);
>   	} else {
> 

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

Regards,

Tvrtko
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