[Linaro-mm-sig] [PATCH 3/9] dma-buf: Warn about dma_fence_chain container rules

[Thomas Hellström]

On 1/20/22 14:27, Christian König wrote:
> Chaining of dma_fence_chain objects is only allowed through the prev
> fence and not through the contained fence.
>
> Warn about that when we create a dma_fence_chain.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>   drivers/dma-buf/dma-fence-chain.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
> index 1b4cb3e5cec9..fa33f6b7f77b 100644
> --- a/drivers/dma-buf/dma-fence-chain.c
> +++ b/drivers/dma-buf/dma-fence-chain.c
> @@ -254,5 +254,13 @@ void dma_fence_chain_init(struct dma_fence_chain *chain,
>   
>   	dma_fence_init(&chain->base, &dma_fence_chain_ops,
>   		       &chain->lock, context, seqno);
> +
> +	/* Chaining dma_fence_chain container together is only allowed through

Nit: Multi-line comment.

Otherwise, Reviewed-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>

> +	 * the prev fence and not through the contained fence.
> +	 *
> +	 * The correct way of handling this is to flatten out the fence
> +	 * structure into a dma_fence_array by the caller instead.
> +	 */
> +	WARN_ON(dma_fence_is_chain(fence));
>   }
>   EXPORT_SYMBOL(dma_fence_chain_init);