Re: [PATCH RFC v2 6/6] mm/memcg: filter out reparented memcgs got from memcgid

[Muchun Song]

> On Sep 1, 2026, at 16:58, Bingfang Guo via B4 Relay <devnull+bingfangguo.tencent.com@xxxxxxxxxx> wrote:
> 
> From: Bingfang Guo <bingfangguo@xxxxxxxxxxx>
> 
> mem_cgroup_from_private_id() looks up the objcg that owns the id and
> returns the objcg's current memcg.  After reparenting, that memcg can
> differ from the one the id originally belonged to.
> 
> Callers such as the list lru and workingset refault code expect to get
> back exactly the memcg referred to by the memcgid, so check that the
> returned memcg still owns the id and return NULL otherwise. In this
> case, make list_lru just skip and workingset tests use the root (as the
> comments said in workingset.c:460).
> 
> Signed-off-by: Bingfang Guo <bingfangguo@xxxxxxxxxxx>

We should move this patch earlier to avoid introducing the problem first
and then fixing it later.

Muchun,
Thanks.