[Intel-gfx] [PATCH 04/10] dma-buf: Report signaled links inside dma-fence-chain

[Lionel Landwerlin]

On 03/04/2020 12:12, Chris Wilson wrote:
> Whenever we walk along the dma-fence-chain, we prune signaled links to
> keep the chain nice and tidy. This leads to situations where we can
> prune a link and report the earlier fence as the target seqno --
> violating our own consistency checks that the seqno is not more advanced
> than the last element in a dma-fence-chain.
>
> Report a NULL fence and success if the seqno has already been signaled.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   drivers/dma-buf/dma-fence-chain.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
> index 3d123502ff12..c435bbba851c 100644
> --- a/drivers/dma-buf/dma-fence-chain.c
> +++ b/drivers/dma-buf/dma-fence-chain.c
> @@ -99,6 +99,12 @@ int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t seqno)
>   		return -EINVAL;
>   
>   	dma_fence_chain_for_each(*pfence, &chain->base) {
> +		if ((*pfence)->seqno < seqno) { /* already signaled */
> +			dma_fence_put(*pfence);
> +			*pfence = NULL;
> +			break;
> +		}
> +


Wouldn't this condition been fulfilled in the previous check? :


chain = to_dma_fence_chain(*pfence);
if (!chain || chain->base.seqno < seqno)
         return -EINVAL;

-Lionel

>   		if ((*pfence)->context != chain->base.context ||
>   		    to_dma_fence_chain(*pfence)->prev_seqno < seqno)
>   			break;
> @@ -222,6 +228,7 @@ EXPORT_SYMBOL(dma_fence_chain_ops);
>    * @chain: the chain node to initialize
>    * @prev: the previous fence
>    * @fence: the current fence
> + * @seqno: the sequence number (syncpt) of the fence within the chain
>    *
>    * Initialize a new chain node and either start a new chain or add the node to
>    * the existing chain of the previous fence.