Re: [PATCH v3 1/2] dma-buf: Split out dma fence array create into alloc and arm functions

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

Am 23.08.24 um 06:54 schrieb Matthew Brost:
> Useful to preallocate dma fence array and then arm in path of reclaim or
> a dma fence.

Exactly that was rejected before because it allows to create circle 
dependencies.

You would need a really really good argument why that is necessary.

Regards,
Christian.

>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   drivers/dma-buf/dma-fence-array.c | 81 ++++++++++++++++++++++---------
>   include/linux/dma-fence-array.h   |  7 +++
>   2 files changed, 66 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
> index c74ac197d5fe..b03e0a87a5cd 100644
> --- a/drivers/dma-buf/dma-fence-array.c
> +++ b/drivers/dma-buf/dma-fence-array.c
> @@ -144,36 +144,38 @@ const struct dma_fence_ops dma_fence_array_ops = {
>   EXPORT_SYMBOL(dma_fence_array_ops);
>   
>   /**
> - * dma_fence_array_create - Create a custom fence array
> + * dma_fence_array_alloc - Allocate a custom fence array
> + * @num_fences:		[in]	number of fences to add in the array
> + *
> + * Return dma fence array on success, NULL on failure
> + */
> +struct dma_fence_array *dma_fence_array_alloc(int num_fences)
> +{
> +	struct dma_fence_array *array;
> +
> +	return kzalloc(struct_size(array, callbacks, num_fences), GFP_KERNEL);
> +}
> +EXPORT_SYMBOL(dma_fence_array_alloc);
> +
> +/**
> + * dma_fence_array_arm - Arm a custom fence array
> + * @array:		[in]	dma fence array to arm
>    * @num_fences:		[in]	number of fences to add in the array
>    * @fences:		[in]	array containing the fences
>    * @context:		[in]	fence context to use
>    * @seqno:		[in]	sequence number to use
>    * @signal_on_any:	[in]	signal on any fence in the array
>    *
> - * Allocate a dma_fence_array object and initialize the base fence with
> - * dma_fence_init().
> - * In case of error it returns NULL.
> - *
> - * The caller should allocate the fences array with num_fences size
> - * and fill it with the fences it wants to add to the object. Ownership of this
> - * array is taken and dma_fence_put() is used on each fence on release.
> - *
> - * If @signal_on_any is true the fence array signals if any fence in the array
> - * signals, otherwise it signals when all fences in the array signal.
> + * Implementation of @dma_fence_array_create without allocation. Useful to arm a
> + * preallocated dma fence fence in the path of reclaim or dma fence signaling.
>    */
> -struct dma_fence_array *dma_fence_array_create(int num_fences,
> -					       struct dma_fence **fences,
> -					       u64 context, unsigned seqno,
> -					       bool signal_on_any)
> +void dma_fence_array_arm(struct dma_fence_array *array,
> +			 int num_fences,
> +			 struct dma_fence **fences,
> +			 u64 context, unsigned seqno,
> +			 bool signal_on_any)
>   {
> -	struct dma_fence_array *array;
> -
> -	WARN_ON(!num_fences || !fences);
> -
> -	array = kzalloc(struct_size(array, callbacks, num_fences), GFP_KERNEL);
> -	if (!array)
> -		return NULL;
> +	WARN_ON(!array || !num_fences || !fences);
>   
>   	array->num_fences = num_fences;
>   
> @@ -200,6 +202,41 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
>   	 */
>   	while (num_fences--)
>   		WARN_ON(dma_fence_is_container(fences[num_fences]));
> +}
> +EXPORT_SYMBOL(dma_fence_array_arm);
> +
> +/**
> + * dma_fence_array_create - Create a custom fence array
> + * @num_fences:		[in]	number of fences to add in the array
> + * @fences:		[in]	array containing the fences
> + * @context:		[in]	fence context to use
> + * @seqno:		[in]	sequence number to use
> + * @signal_on_any:	[in]	signal on any fence in the array
> + *
> + * Allocate a dma_fence_array object and initialize the base fence with
> + * dma_fence_init().
> + * In case of error it returns NULL.
> + *
> + * The caller should allocate the fences array with num_fences size
> + * and fill it with the fences it wants to add to the object. Ownership of this
> + * array is taken and dma_fence_put() is used on each fence on release.
> + *
> + * If @signal_on_any is true the fence array signals if any fence in the array
> + * signals, otherwise it signals when all fences in the array signal.
> + */
> +struct dma_fence_array *dma_fence_array_create(int num_fences,
> +					       struct dma_fence **fences,
> +					       u64 context, unsigned seqno,
> +					       bool signal_on_any)
> +{
> +	struct dma_fence_array *array;
> +
> +	array = dma_fence_array_alloc(num_fences);
> +	if (!array)
> +		return NULL;
> +
> +	dma_fence_array_arm(array, num_fences, fences,
> +			    context, seqno, signal_on_any);
>   
>   	return array;
>   }
> diff --git a/include/linux/dma-fence-array.h b/include/linux/dma-fence-array.h
> index 29c5650c1038..3466ffc4b803 100644
> --- a/include/linux/dma-fence-array.h
> +++ b/include/linux/dma-fence-array.h
> @@ -79,6 +79,13 @@ to_dma_fence_array(struct dma_fence *fence)
>   	for (index = 0, fence = dma_fence_array_first(head); fence;	\
>   	     ++(index), fence = dma_fence_array_next(head, index))
>   
> +struct dma_fence_array *dma_fence_array_alloc(int num_fences);
> +void dma_fence_array_arm(struct dma_fence_array *array,
> +			 int num_fences,
> +			 struct dma_fence **fences,
> +			 u64 context, unsigned seqno,
> +			 bool signal_on_any);
> +
>   struct dma_fence_array *dma_fence_array_create(int num_fences,
>   					       struct dma_fence **fences,
>   					       u64 context, unsigned seqno,