Re: [PATCH 03/11] cgroup: move cgroup_rstat from cgroup to cgroup_subsys_state

[Shakeel Butt <shakeel.butt@linux.dev>]

On Mon, Feb 17, 2025 at 07:14:40PM -0800, JP Kobryn wrote:
[...]
> @@ -3240,6 +3234,12 @@ static int cgroup_apply_control_enable(struct cgroup *cgrp)
>  				css = css_create(dsct, ss);
>  				if (IS_ERR(css))
>  					return PTR_ERR(css);

Since rstat is part of css, why not cgroup_rstat_init() inside
css_create()?

> +
> +				if (css->ss && css->ss->css_rstat_flush) {
> +					ret = cgroup_rstat_init(css);
> +					if (ret)
> +						goto err_out;
> +				}
>  			}
>  
>  			WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
> @@ -3253,6 +3253,21 @@ static int cgroup_apply_control_enable(struct cgroup *cgrp)
>  	}
>  
>  	return 0;

Why not the following cleanup in css_kill()? If you handle it in
css_kill(), you don't need this special handling.

> +
> +err_out:
> +	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
> +		for_each_subsys(ss, ssid) {
> +			struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
> +
> +			if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
> +				continue;
> +
> +			if (css && css->ss && css->ss->css_rstat_flush)
> +				cgroup_rstat_exit(css);
> +		}
> +	}
> +
> +	return ret;
>  }