[PATCH] drm/syncobj: Deal with signalled fences in transfer.

[Christian König]

Am 07.12.21 um 02:32 schrieb Bas Nieuwenhuizen:
> See the comments in the code. Basically if the seqno is already
> signalled then we get a NULL fence. If we then put the NULL fence
> in a binary syncobj it counts as unsignalled, making that syncobj
> pretty much useless for all expected uses.
>
> Not 100% sure about the transfer to a timeline syncobj but I
> believe it is needed there too, as AFAICT the add_point function
> assumes the fence isn't NULL.
>
> Fixes: ea569910cbab ("drm/syncobj: add transition iotcls between binary and timeline v2")
> Cc: stable at vger.kernel.org
> Signed-off-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>

Reviewed-by: Christian König <christian.koenig at amd.com>

Going to push that to drm-misc-fixes later today if nobody objects in 
the meantime.

> ---
>   drivers/gpu/drm/drm_syncobj.c | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index fdd2ec87cdd1..eb28a40400d2 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -861,6 +861,19 @@ static int drm_syncobj_transfer_to_timeline(struct drm_file *file_private,
>   				     &fence);
>   	if (ret)
>   		goto err;
> +
> +	/* If the requested seqno is already signaled drm_syncobj_find_fence may
> +	 * return a NULL fence. To make sure the recipient gets signalled, use
> +	 * a new fence instead.
> +	 */
> +	if (!fence) {
> +		fence = dma_fence_allocate_private_stub();
> +		if (!fence) {
> +			ret = -ENOMEM;
> +			goto err;
> +		}
> +	}
> +
>   	chain = kzalloc(sizeof(struct dma_fence_chain), GFP_KERNEL);
>   	if (!chain) {
>   		ret = -ENOMEM;
> @@ -890,6 +903,19 @@ drm_syncobj_transfer_to_binary(struct drm_file *file_private,
>   				     args->src_point, args->flags, &fence);
>   	if (ret)
>   		goto err;
> +
> +	/* If the requested seqno is already signaled drm_syncobj_find_fence may
> +	 * return a NULL fence. To make sure the recipient gets signalled, use
> +	 * a new fence instead.
> +	 */
> +	if (!fence) {
> +		fence = dma_fence_allocate_private_stub();
> +		if (!fence) {
> +			ret = -ENOMEM;
> +			goto err;
> +		}
> +	}
> +
>   	drm_syncobj_replace_fence(binary_syncobj, fence);
>   	dma_fence_put(fence);
>   err: