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Date:   Thu, 11 Aug 2022 10:49:13 +0800
From:   Yafang Shao <>
To:     Shakeel Butt <>
Cc:     Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Andrii Nakryiko <>, Martin Lau <>,
        Song Liu <>, Yonghong Song <>,
        john fastabend <>,
        KP Singh <>,
        Stanislav Fomichev <>,
        Hao Luo <>,,
        Johannes Weiner <>,
        Michal Hocko <>,
        Roman Gushchin <>,
        Muchun Song <>,
        Andrew Morton <>,
        netdev <>, bpf <>,
        Linux MM <>
Subject: Re: [PATCH bpf-next 05/15] bpf: Fix incorrect mem_cgroup_put

On Thu, Aug 11, 2022 at 1:07 AM Shakeel Butt <> wrote:
> On Wed, Aug 10, 2022 at 03:18:30PM +0000, Yafang Shao wrote:
> > The memcg may be the root_mem_cgroup, in which case we shouldn't put it.
> No, it is ok to put root_mem_cgroup. css_put already handles the root
> cgroups.

Ah, this commit log doesn't describe the issue clearly. I should improve it.
The issue is that in bpf_map_get_memcg() it doesn't get the objcg if
map->objcg is NULL (that can happen if the map belongs to the root
memcg), so we shouldn't put the objcg if map->objcg is NULL neither in
Maybe the change below would be more reasonable ?

+static void bpf_map_put_memcg(const struct bpf_map *map, struct
mem_cgroup *memcg)
+       if (map->objcg)
+           mem_cgroup_put(memcg);


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