Re: [PATCH 1/8] drm/amdgpu: use GEM references instead of TTMs

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Tue, Jul 23, 2024 at 02:17:43PM +0200, Christian König wrote:
> Instead of a TTM reference grab a GEM reference whenever necessary.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Felix Kuehling <felix.kuehling@amd.com>
> Cc: amd-gfx@lists.freedesktop.org

I was worried that changing the refcounting for the mmu_interval_notifier
that this patch does could result in a use-after-free, but the mmu
notifier code already does the required amount of mmgrab/mmdrop, so we're
good.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Cheers, Sima

> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c    | 8 ++++----
>  drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 7 ++-----
>  2 files changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> index 67c234bcf89f..6be3d7cd1c51 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -87,11 +87,11 @@ static const struct vm_operations_struct amdgpu_gem_vm_ops = {
>  
>  static void amdgpu_gem_object_free(struct drm_gem_object *gobj)
>  {
> -	struct amdgpu_bo *robj = gem_to_amdgpu_bo(gobj);
> +	struct amdgpu_bo *aobj = gem_to_amdgpu_bo(gobj);
>  
> -	if (robj) {
> -		amdgpu_hmm_unregister(robj);
> -		amdgpu_bo_unref(&robj);
> +	if (aobj) {
> +		amdgpu_hmm_unregister(aobj);
> +		ttm_bo_put(&aobj->tbo);
>  	}
>  }
>  
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> index 8d8c39be6129..6c187e310034 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> @@ -853,7 +853,7 @@ struct amdgpu_bo *amdgpu_bo_ref(struct amdgpu_bo *bo)
>  	if (bo == NULL)
>  		return NULL;
>  
> -	ttm_bo_get(&bo->tbo);
> +	drm_gem_object_get(&bo->tbo.base);
>  	return bo;
>  }
>  
> @@ -865,13 +865,10 @@ struct amdgpu_bo *amdgpu_bo_ref(struct amdgpu_bo *bo)
>   */
>  void amdgpu_bo_unref(struct amdgpu_bo **bo)
>  {
> -	struct ttm_buffer_object *tbo;
> -
>  	if ((*bo) == NULL)
>  		return;
>  
> -	tbo = &((*bo)->tbo);
> -	ttm_bo_put(tbo);
> +	drm_gem_object_get(&(*bo)->tbo.base);
>  	*bo = NULL;
>  }
>  
> -- 
> 2.34.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch