Re: [PATCH 4/4] memcg: move memcg private ID refcount to objcg

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

On Fri, Sep 18, 2026 at 05:18:43PM +0800, Bingfang Guo via B4 Relay wrote:
> From: Bingfang Guo <bingfangguo@tencent.com>
> 
> diff --git a/mm/workingset.c b/mm/workingset.c
> index 8412f4840ae35..7e4fbc5a786d6 100644
> --- a/mm/workingset.c
> +++ b/mm/workingset.c
> @@ -281,6 +281,9 @@ static bool lru_gen_test_recent(void *shadow, struct lruvec **lruvec,
>  	unpack_shadow(shadow, &memcg_id, &pgdat, token, workingset);
>  
>  	memcg = mem_cgroup_from_private_id(memcg_id);
> +	if (!memcg)
> +		return false;

You can not return here without initializing *lruvec as it might be used in the
caller. Also mem_cgroup_lruvec() can handle null memcg and will substitute with
root_mem_cgroup.

> +
>  	*lruvec = mem_cgroup_lruvec(memcg, pgdat);
>  
>  	max_seq = READ_ONCE((*lruvec)->lrugen.max_seq);
> @@ -470,7 +473,7 @@ bool workingset_test_recent(void *shadow, bool file, bool *workingset,
>  	 * configurations instead.
>  	 */
>  	eviction_memcg = mem_cgroup_from_private_id(memcgid);
> -	if (!mem_cgroup_tryget(eviction_memcg))
> +	if (eviction_memcg && !mem_cgroup_tryget(eviction_memcg))
>  		eviction_memcg = NULL;
>  	rcu_read_unlock();
>  
> 
> -- 
> 2.43.7
> 
>