Re: [PATCH 3/5] dma-buf: return only unsignaled fences in dma_fence_unwrap_for_each v3

[Karolina Drobnik <karolina.drobnik@intel.com>]

Hi Christian,

I'm sorry for digging this one out so late.

On 06.05.2022 16:10, Christian König wrote:
> dma_fence_chain containers cleanup signaled fences automatically, so
> filter those out from arrays as well.
> 
> v2: fix missing walk over the array
> v3: massively simplify the patch and actually update the description.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>   include/linux/dma-fence-unwrap.h | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
> index e7c219da4ed7..a4d342fef8e0 100644
> --- a/include/linux/dma-fence-unwrap.h
> +++ b/include/linux/dma-fence-unwrap.h
> @@ -43,9 +43,13 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
>    * Unwrap dma_fence_chain and dma_fence_array containers and deep dive into all
>    * potential fences in them. If @head is just a normal fence only that one is
>    * returned.
> + *
> + * Note that signalled fences are opportunistically filtered out, which
> + * means the iteration is potentially over no fence at all.
>    */
>   #define dma_fence_unwrap_for_each(fence, cursor, head)			\
>   	for (fence = dma_fence_unwrap_first(head, cursor); fence;	\
> -	     fence = dma_fence_unwrap_next(cursor))
> +	     fence = dma_fence_unwrap_next(cursor))			\
> +		if (!dma_fence_is_signaled(fence))
>   
>   #endif

It looks like this particular patch affects merging Sync Fences, which 
is reflected by failing IGT test (igt@sw_sync)[1]. The failing subtests are:
   - sync_merge - merging different fences on the same timeline, neither
		 single nor merged fences are signaled

   - sync_merge_same - merging the fence with itself on the same
		 timeline, the fence didn't signal at all

   - sync_multi_timeline_wait - merging different fences on different
		 timelines; the subtest checks if counting fences of
		 various states works. Currently, it can only see 2
		 active fences, 0 signaling (should be 2 active,
		 1 signaling)

Reverting this commit on the top of drm-tip fixes the issue, but I'm not 
sure if it wouldn't impact other places in the code. Please let me know 
if I can be of any help.

All the best,
Karolina

---------------------
[1] - reproducible locally, but can be also seen in the CI:
https://intel-gfx-ci.01.org/tree/drm-tip/index.html?testfilter=igt@sw_sync