[PATCH 3/4] dma-buf: Warn about dma_fence_chain container rules

[Daniel Vetter]

On Wed, Jan 19, 2022 at 02:43:38PM +0100, 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>
> ---
>  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
> +	 * 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));

At first I was worried that you'd leave a chain fence in the array fence
as an option, but we exclude that with the previous patch.

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

>  }
>  EXPORT_SYMBOL(dma_fence_chain_init);
> -- 
> 2.25.1
> 

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