Re: [PATCH v16 02/16] cgroup/misc: Add per resource callbacks for CSS events

[Huang, Kai]

On Tue, 2024-08-20 at 18:53 -0700, Haitao Huang wrote:
>  /**
>   * misc_cg_alloc() - Allocate misc cgroup.
>   * @parent_css: Parent cgroup.
> @@ -451,20 +519,25 @@ static struct cftype misc_cg_files[] = {
>  static struct cgroup_subsys_state *
>  misc_cg_alloc(struct cgroup_subsys_state *parent_css)
>  {
> -	enum misc_res_type i;
> -	struct misc_cg *cg;
> +	struct misc_cg *parent_cg, *cg;
> +	int ret;
>  
>  	if (!parent_css) {
> +		parent_cg = &root_cg;
>  		cg = &root_cg;
>  	} else {
>  		cg = kzalloc(sizeof(*cg), GFP_KERNEL);
>  		if (!cg)
>  			return ERR_PTR(-ENOMEM);
> +		parent_cg = css_misc(parent_css);
>  	}
>  
> -	for (i = 0; i < MISC_CG_RES_TYPES; i++) {
> -		WRITE_ONCE(cg->res[i].max, MAX_NUM);
> -		atomic64_set(&cg->res[i].usage, 0);
> +	ret = _misc_cg_res_alloc(cg);
> +	if (ret) {
> +		if (likely(parent_css))
> +			kfree(cg);
> +
> +		return ERR_PTR(ret);
>  	}
>  
>  	return &cg->css;

What's the purpose of @parent_cg?

# make kernel/cgroup/ W=1
...
kernel/cgroup/misc.c: In function ‘misc_cg_alloc’:
kernel/cgroup/misc.c:522:25: warning: variable ‘parent_cg’ set but not used [-
Wunused-but-set-variable]
  522 |         struct misc_cg *parent_cg, *cg;
      |                         ^~~~~~~~~