Re: [PATCH] llist: add [READ|WRITE]_ONCE tags for llist_node

[Tejun Heo]

Hello,

On Thu, Jun 26, 2025 at 04:38:18PM -0700, Shakeel Butt wrote:
> diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
> index c8a48cf83878..02258b43abb3 100644
> --- a/kernel/cgroup/rstat.c
> +++ b/kernel/cgroup/rstat.c
> @@ -86,8 +86,12 @@ __bpf_kfunc void css_rstat_updated(struct cgroup_subsys_state *css, int cpu)
>  		return;
>  
>  	rstatc = css_rstat_cpu(css, cpu);
> -	/* If already on list return. */
> -	if (llist_on_list(&rstatc->lnode))
> +	/*
> +	 * If already on list return.
> +	 *
> +	 * TODO: add detailed comment on the potential race.
> +	 */
> +	if (data_race(llist_on_list(&rstatc->lnode)))
>  		return;

Yeah, also in the functdion comment, explain that if avoiding such races is
important enough to justify the overhead, the caller can put smp_mb() before
calling css_rstat_updated().

Thanks.

-- 
tejun