[PATCH] drm/ttm: Warn on pinning without holding a reference

[Huang Rui]

On Wed, Oct 28, 2020 at 07:31:20PM +0800, Daniel Vetter wrote:
> Not technically a problem for ttm, but very likely a driver bug and
> pretty big time confusing for reviewing code.
> 
> So warn about it, both at cleanup time (so we catch these for sure)
> and at pin/unpin time (so we know who's the culprit).
> 
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>

Reviewed-by: Huang Rui <ray.huang at amd.com>

> Cc: Christian Koenig <christian.koenig at amd.com>
> Cc: Huang Rui <ray.huang at amd.com>
> ---
>  drivers/gpu/drm/ttm/ttm_bo.c | 2 +-
>  include/drm/ttm/ttm_bo_api.h | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index f51b5e20fa17..a011072ab61d 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -509,7 +509,7 @@ static void ttm_bo_release(struct kref *kref)
>  		 * shrinkers, now that they are queued for
>  		 * destruction.
>  		 */
> -		if (bo->pin_count) {
> +		if (WARN_ON(bo->pin_count)) {
>  			bo->pin_count = 0;
>  			ttm_bo_del_from_lru(bo);
>  			ttm_bo_add_mem_to_lru(bo, &bo->mem);
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index 37102e45e496..b45aee23d7d0 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -571,6 +571,7 @@ static inline bool ttm_bo_uses_embedded_gem_object(struct ttm_buffer_object *bo)
>  static inline void ttm_bo_pin(struct ttm_buffer_object *bo)
>  {
>  	dma_resv_assert_held(bo->base.resv);
> +	WARN_ON_ONCE(!kref_read(&bo->kref));
>  	++bo->pin_count;
>  }
>  
> @@ -584,6 +585,7 @@ static inline void ttm_bo_unpin(struct ttm_buffer_object *bo)
>  {
>  	dma_resv_assert_held(bo->base.resv);
>  	WARN_ON_ONCE(!bo->pin_count);
> +	WARN_ON_ONCE(!kref_read(&bo->kref));
>  	--bo->pin_count;
>  }
>  
> -- 
> 2.28.0
>