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    Subject[PATCH] mm: memcontrol: fix forget to obtain the ref to objcg in split_page_memcg
    Date
    Christian Borntraeger reported a warning about "percpu ref
    (obj_cgroup_release) <= 0 (-1) after switching to atomic".
    Because we forgot to obtain the reference to the objcg and
    wrongly obtain the reference of memcg.

    Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
    Signed-off-by: Muchun Song <songmuchun@bytedance.com>
    ---
    include/linux/memcontrol.h | 6 ++++++
    mm/memcontrol.c | 6 +++++-
    2 files changed, 11 insertions(+), 1 deletion(-)

    diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
    index 0e8907957227..c960fd49c3e8 100644
    --- a/include/linux/memcontrol.h
    +++ b/include/linux/memcontrol.h
    @@ -804,6 +804,12 @@ static inline void obj_cgroup_get(struct obj_cgroup *objcg)
    percpu_ref_get(&objcg->refcnt);
    }

    +static inline void obj_cgroup_get_many(struct obj_cgroup *objcg,
    + unsigned long nr)
    +{
    + percpu_ref_get_many(&objcg->refcnt, nr);
    +}
    +
    static inline void obj_cgroup_put(struct obj_cgroup *objcg)
    {
    percpu_ref_put(&objcg->refcnt);
    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index c0b83a396299..64ada9e650a5 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -3133,7 +3133,11 @@ void split_page_memcg(struct page *head, unsigned int nr)

    for (i = 1; i < nr; i++)
    head[i].memcg_data = head->memcg_data;
    - css_get_many(&memcg->css, nr - 1);
    +
    + if (PageMemcgKmem(head))
    + obj_cgroup_get_many(__page_objcg(head), nr - 1);
    + else
    + css_get_many(&memcg->css, nr - 1);
    }

    #ifdef CONFIG_MEMCG_SWAP
    --
    2.11.0
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