[PATCH v3] drm: modify drm_global_item_ref to avoid two times of writing ref->object

[Chris Wilson]

On Wed, Sep 07, 2016 at 10:07:57PM -0400, Huang Rui wrote:
> In previous drm_global_item_ref, there are two times of writing
> ref->object if item->refcount is 0. So this patch does a minor update
> to put alloc and init ref firstly, and then to modify the item of glob
> array. Use "else" to avoid two times of writing ref->object. It can
> make the code logic more clearly.
> 
> Signed-off-by: Huang Rui <ray.huang at amd.com>
> ---
> 
> Changes from V2 -> V3:
> - Use duplicate mutex release to avoid "goto" in non-error patch.
> - Rename error label
> 
> ---
>  drivers/gpu/drm/drm_global.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_global.c b/drivers/gpu/drm/drm_global.c
> index 3d2e91c..b404287 100644
> --- a/drivers/gpu/drm/drm_global.c
> +++ b/drivers/gpu/drm/drm_global.c
> @@ -65,30 +65,34 @@ void drm_global_release(void)
>  
>  int drm_global_item_ref(struct drm_global_reference *ref)
>  {
> -	int ret;
> +	int ret = 0;
>  	struct drm_global_item *item = &glob[ref->global_type];
>  
>  	mutex_lock(&item->mutex);
>  	if (item->refcount == 0) {
> -		item->object = kzalloc(ref->size, GFP_KERNEL);
> -		if (unlikely(item->object == NULL)) {
> +		ref->object = kzalloc(ref->size, GFP_KERNEL);

So the item refcount is 0, we operate on ref, whereas previous we
inspected item and operated on item. Not an improvement.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre