Re: [Intel-gfx] [PATCH 2/2] dma-buf: fix dma-fence-chain out of order test

["Christian König" <christian.koenig@amd.com>]

Am 25.06.20 um 14:34 schrieb Lionel Landwerlin:
> There was probably a misunderstand on how the dma-fence-chain is
> supposed to work or what dma_fence_chain_find_seqno() is supposed to
> return.
>
> dma_fence_chain_find_seqno() is here to give us the fence to wait upon
> for a particular point in the timeline. The timeline progresses only
> when all the points prior to a given number have completed.
>
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> Fixes: dc2f7e67a28a5c ("dma-buf: Exercise dma-fence-chain under selftests")

Acked-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/dma-buf/st-dma-fence-chain.c | 43 ++++++++++++++--------------
>   1 file changed, 21 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/dma-buf/st-dma-fence-chain.c b/drivers/dma-buf/st-dma-fence-chain.c
> index 5d45ba7ba3cd..9525f7f56119 100644
> --- a/drivers/dma-buf/st-dma-fence-chain.c
> +++ b/drivers/dma-buf/st-dma-fence-chain.c
> @@ -318,15 +318,16 @@ static int find_out_of_order(void *arg)
>   		goto err;
>   	}
>   
> -	if (fence && fence != fc.chains[1]) {
> +	/*
> +	 * We signaled the middle fence (2) of the 1-2-3 chain. The behavior
> +	 * of the dma-fence-chain is to make us wait for all the fences up to
> +	 * the point we want. Since fence 1 is still not signaled, this what
> +	 * we should get as fence to wait upon (fence 2 being garbage
> +	 * collected during the traversal of the chain).
> +	 */
> +	if (fence != fc.chains[0]) {
>   		pr_err("Incorrect chain-fence.seqno:%lld reported for completed seqno:2\n",
> -		       fence->seqno);
> -
> -		dma_fence_get(fence);
> -		err = dma_fence_chain_find_seqno(&fence, 2);
> -		dma_fence_put(fence);
> -		if (err)
> -			pr_err("Reported %d for finding self!\n", err);
> +		       fence ? fence->seqno : 0);
>   
>   		err = -EINVAL;
>   	}
> @@ -415,20 +416,18 @@ static int __find_race(void *arg)
>   		if (!fence)
>   			goto signal;
>   
> -		err = dma_fence_chain_find_seqno(&fence, seqno);
> -		if (err) {
> -			pr_err("Reported an invalid fence for find-self:%d\n",
> -			       seqno);
> -			dma_fence_put(fence);
> -			break;
> -		}
> -
> -		if (fence->seqno < seqno) {
> -			pr_err("Reported an earlier fence.seqno:%lld for seqno:%d\n",
> -			       fence->seqno, seqno);
> -			err = -EINVAL;
> -			dma_fence_put(fence);
> -			break;
> +		/*
> +		 * We can only find ourselves if we are on fence we were
> +		 * looking for.
> +		 */
> +		if (fence->seqno == seqno) {
> +			err = dma_fence_chain_find_seqno(&fence, seqno);
> +			if (err) {
> +				pr_err("Reported an invalid fence for find-self:%d\n",
> +				       seqno);
> +				dma_fence_put(fence);
> +				break;
> +			}
>   		}
>   
>   		dma_fence_put(fence);

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