[PATCH 03/23] dma-buf: add dma_resv_get_singleton v2

[Christian König]

Daniel any more comments on this one here?

It's the prerequisite to a bunch of other patches and I would like to 
get it out of my feet.

Thanks,
Christian.

Am 21.03.22 um 14:58 schrieb Christian König:
> Add a function to simplify getting a single fence for all the fences in
> the dma_resv object.
>
> v2: fix ref leak in error handling
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>   drivers/dma-buf/dma-resv.c | 52 ++++++++++++++++++++++++++++++++++++++
>   include/linux/dma-resv.h   |  2 ++
>   2 files changed, 54 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 5001e9b4420a..c09fd8da0c85 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -34,6 +34,7 @@
>    */
>   
>   #include <linux/dma-resv.h>
> +#include <linux/dma-fence-array.h>
>   #include <linux/export.h>
>   #include <linux/mm.h>
>   #include <linux/sched/mm.h>
> @@ -650,6 +651,57 @@ int dma_resv_get_fences(struct dma_resv *obj, bool write,
>   }
>   EXPORT_SYMBOL_GPL(dma_resv_get_fences);
>   
> +/**
> + * dma_resv_get_singleton - Get a single fence for all the fences
> + * @obj: the reservation object
> + * @write: true if we should return all fences
> + * @fence: the resulting fence
> + *
> + * Get a single fence representing all the fences inside the resv object.
> + * Returns either 0 for success or -ENOMEM.
> + *
> + * Warning: This can't be used like this when adding the fence back to the resv
> + * object since that can lead to stack corruption when finalizing the
> + * dma_fence_array.
> + */
> +int dma_resv_get_singleton(struct dma_resv *obj, bool write,
> +			   struct dma_fence **fence)
> +{
> +	struct dma_fence_array *array;
> +	struct dma_fence **fences;
> +	unsigned count;
> +	int r;
> +
> +	r = dma_resv_get_fences(obj, write, &count, &fences);
> +        if (r)
> +		return r;
> +
> +	if (count == 0) {
> +		*fence = NULL;
> +		return 0;
> +	}
> +
> +	if (count == 1) {
> +		*fence = fences[0];
> +		kfree(fences);
> +		return 0;
> +	}
> +
> +	array = dma_fence_array_create(count, fences,
> +				       dma_fence_context_alloc(1),
> +				       1, false);
> +	if (!array) {
> +		while (count--)
> +			dma_fence_put(fences[count]);
> +		kfree(fences);
> +		return -ENOMEM;
> +	}
> +
> +	*fence = &array->base;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(dma_resv_get_singleton);
> +
>   /**
>    * dma_resv_wait_timeout - Wait on reservation's objects
>    * shared and/or exclusive fences.
> diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
> index 202cc65d0621..08512c1e215d 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -449,6 +449,8 @@ void dma_resv_replace_fences(struct dma_resv *obj, uint64_t context,
>   void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence);
>   int dma_resv_get_fences(struct dma_resv *obj, bool write,
>   			unsigned int *num_fences, struct dma_fence ***fences);
> +int dma_resv_get_singleton(struct dma_resv *obj, bool write,
> +			   struct dma_fence **fence);
>   int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src);
>   long dma_resv_wait_timeout(struct dma_resv *obj, bool wait_all, bool intr,
>   			   unsigned long timeout);