Re: [PATCH mm-unstable v3 4/5] mm: restart if multiple traversals raced

[Kinsey Ho]

On Fri, Aug 30, 2024 at 3:04 AM Hugh Dickins <hughd@xxxxxxxxxx> wrote:
>
> mm-unstable commit 954dd0848c61 needs the fix below to be merged in;
> but the commit after it (the 5/5) then renames "memcg" to "next",
> so that one has to be adjusted too.
>
> [PATCH] mm: restart if multiple traversals raced: fix
>
> mem_cgroup_iter() reset memcg to NULL before the goto restart, so that
> goto out_unlock does not then return an ungotten memcg, causing oopses
> on stale memcg in many places (often in memcg_rstat_updated()).
>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> ---
>  mm/memcontrol.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6f66ac0ad4f0..dd82dd1e1f0a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1049,6 +1049,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
>                 if (cmpxchg(&iter->position, pos, memcg) != pos) {
>                         if (css && css != &root->css)
>                                 css_put(css);
> +                       memcg = NULL;
>                         goto restart;
>                 }
>
> --
> 2.35.3

Hi Andrew,

Would you prefer that I resend the series with Hugh's fix inserted?

Acked-by: Kinsey Ho <kinseyho@xxxxxxxxxx>