Re: [PATCH 5/7] drm/syncobj: Avoid temporary allocation in drm_syncobj_timeline_signal_ioctl

["Maíra Canal" <mcanal@igalia.com>]

Hi Tvrtko,

On 18/03/25 12:54, Tvrtko Ursulin wrote:
> We can avoid one of the two temporary allocations if we read the userspace
> supplied timeline points as we go along.
> 
> The only new complication is to unwind unused fence chains on the error
> path, but even that code was already present in the function.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>

Reviewed-by: Maíra Canal <mcanal@igalia.com>

Best Regards,
- Maíra

> ---
>   drivers/gpu/drm/drm_syncobj.c | 46 +++++++++++++++--------------------
>   1 file changed, 20 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 74d1dc0d1f8b..b4563c696056 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -1557,10 +1557,10 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
>   				  struct drm_file *file_private)
>   {
>   	struct drm_syncobj_timeline_array *args = data;
> +	uint64_t __user *points = u64_to_user_ptr(args->points);
> +	uint32_t i, j, count = args->count_handles;
>   	struct drm_syncobj **syncobjs;
>   	struct dma_fence_chain **chains;
> -	uint64_t *points;
> -	uint32_t i, j;
>   	int ret;
>   
>   	if (!drm_core_check_feature(dev, DRIVER_SYNCOBJ_TIMELINE))
> @@ -1572,33 +1572,22 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
>   	if (args->count_handles == 0)
>   		return -EINVAL;
>   
> +	if (!access_ok(points, count * sizeof(*points)))
> +		return -EFAULT;
> +
>   	ret = drm_syncobj_array_find(file_private,
>   				     u64_to_user_ptr(args->handles),
> -				     args->count_handles,
> +				     count,
>   				     &syncobjs);
>   	if (ret < 0)
>   		return ret;
>   
> -	points = kmalloc_array(args->count_handles, sizeof(*points),
> -			       GFP_KERNEL);
> -	if (!points) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> -	if (!u64_to_user_ptr(args->points)) {
> -		memset(points, 0, args->count_handles * sizeof(uint64_t));
> -	} else if (copy_from_user(points, u64_to_user_ptr(args->points),
> -				  sizeof(uint64_t) * args->count_handles)) {
> -		ret = -EFAULT;
> -		goto err_points;
> -	}
> -
> -	chains = kmalloc_array(args->count_handles, sizeof(void *), GFP_KERNEL);
> +	chains = kmalloc_array(count, sizeof(void *), GFP_KERNEL);
>   	if (!chains) {
>   		ret = -ENOMEM;
> -		goto err_points;
> +		goto out;
>   	}
> -	for (i = 0; i < args->count_handles; i++) {
> +	for (i = 0; i < count; i++) {
>   		chains[i] = dma_fence_chain_alloc();
>   		if (!chains[i]) {
>   			for (j = 0; j < i; j++)
> @@ -1608,19 +1597,24 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
>   		}
>   	}
>   
> -	for (i = 0; i < args->count_handles; i++) {
> +	for (i = 0; i < count; i++) {
>   		struct dma_fence *fence = dma_fence_get_stub();
> +		u64 point = 0;
>   
> -		drm_syncobj_add_point(syncobjs[i], chains[i],
> -				      fence, points[i]);
> +		if (points && __get_user(point, points++)) {
> +			ret =  -EFAULT;
> +			for (j = i; j < count; j++)
> +				dma_fence_chain_free(chains[j]);
> +			goto err_chains;
> +		}
> +
> +		drm_syncobj_add_point(syncobjs[i], chains[i], fence, point);
 >   		dma_fence_put(fence);>   	}
>   err_chains:
>   	kfree(chains);
> -err_points:
> -	kfree(points);
>   out:
> -	drm_syncobj_array_free(syncobjs, args->count_handles);
> +	drm_syncobj_array_free(syncobjs, count);
>   
>   	return ret;
>   }