Re: [PATCH 2/4] dma-buf: warn about dma_fence_array container rules

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jan 19, 2022 at 02:43:37PM +0100, Christian König wrote:
> It's not allowed to nest another dma_fence container into a dma_fence_array
> or otherwise we can run into recursion.
> 
> Warn about that when we create a dma_fence_array.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/dma-fence-array.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
> index 3e07f961e2f3..4bfbcb885bbc 100644
> --- a/drivers/dma-buf/dma-fence-array.c
> +++ b/drivers/dma-buf/dma-fence-array.c
> @@ -176,6 +176,19 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
>  
>  	array->base.error = PENDING_ERROR;
>  
> +	/* dma_fence_array objects should never contain any other fence
> +	 * containers or otherwise we run into recursion and potential kernel
> +	 * stack overflow on operations on the dma_fence_array.
> +	 *
> +	 * The correct way of handling this is to flatten out the array by the
> +	 * caller instead.
> +	 *
> +	 * Enforce this here by checking that we don't create a dma_fence_array
> +	 * with any container inside.
> +	 */
> +	while (seqno--)
> +		WARN_ON(dma_fence_is_container(fences[seqno]));

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

> +
>  	return array;
>  }
>  EXPORT_SYMBOL(dma_fence_array_create);
> -- 
> 2.25.1
> 

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