Re: [PATCH] mm: list_lru: don't use a new memcg's lists for an offline memcg

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

On Fri, Nov 13, 2026 at 12:15:11AM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential
> issue to consider:
> - [High] mm: list_lru: missing mlru->memcg check in
>   memcg_list_lru_allocated()
> --
> 
> commit d213b82b7b4ca4978c858df10a2a8cdea14626e4
> Author: Shakeel Butt <shakeel.butt@linux.dev>
> 
> mm: list_lru: don't use a new memcg's lists for an offline memcg
> 
> This commit records the owning memcg in struct list_lru_memcg and checks it
> in list_lru_from_memcg() so that an offline memcg whose kmemcg_id was reused
> does not use the new memcg's lists.
> 
> > diff --git a/mm/list_lru.c b/mm/list_lru.c
> > index d1d256822ccc7..937dbf239c9d4 100644
> > --- a/mm/list_lru.c
> > +++ b/mm/list_lru.c
> > @@ -72,12 +72,15 @@ static int lru_shrinker_id(struct list_lru *lru)
> >  }
> >  
> >  static inline struct list_lru_one *
> > -list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
> > +list_lru_from_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg)
> >  {
> > +	int idx = memcg_kmem_id(memcg);
> > +
> >  	if (list_lru_memcg_aware(lru) && idx >= 0) {
> >  		struct list_lru_memcg *mlru = xa_load(&lru->xa, idx);
> >  
> > -		return mlru ? &mlru->node[nid] : NULL;
> > +		/* Lists at a reused index belong to another memcg. */
> > +		return mlru && mlru->memcg == memcg ? &mlru->node[nid] : NULL;
> >  	}
> >  	return &lru->node[nid].lru;
> >  }
> 
> [ ... ]
> 
> > @@ -602,6 +604,8 @@ static int __memcg_list_lru_alloc(struct mem_cgroup *memcg,
> >  			if (!mlru)
> >  				return -ENOMEM;
> >  		}
> > +		/* Set before the lists are published, and never changed after. */
> > +		mlru->memcg = pos;
> >  		xas_set(&xas, pos->kmemcg_id);
> >  		do {
> >  			xas_lock_irqsave(&xas, flags);
> 
> [Severity: High]
> Does memcg_list_lru_allocated() also need to check mlru->memcg == memcg?

Yes this is correct and Andrew already have a fix for this.