Re: [PATCH] mm: memcontrol: fix swap counter leak from offline cgroup

[Johannes Weiner]

On Thu, Mar 06, 2025 at 10:54:12AM +0800, Kairui Song wrote:
> On Thu, Mar 6, 2025 at 10:32 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
> >
> > The commit 6769183166b3 has removed the parameter of id from
> > swap_cgroup_record() and get the memcg id from
> > mem_cgroup_id(folio_memcg(folio)). However, the caller of it
> > may update a different memcg's counter instead of
> > folio_memcg(folio). E.g. in the caller of mem_cgroup_swapout(),
> > @swap_memcg could be different with @memcg and update the counter
> > of @swap_memcg, but swap_cgroup_record() records the wrong memcg's
> > ID. When it is uncharged from __mem_cgroup_uncharge_swap(), the
> > swap counter will leak since the wrong recorded ID. Fix it by
> > bring the parameter of id back.
> >
> > Fixes: 6769183166b3 ("mm/swap_cgroup: decouple swap cgroup recording and clearing")
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Looking at the original commit again, we also should do this:

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