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    Subject[PATCH 5.11 702/775] mm: memcontrol: fix get_active_memcg return value
    Date
    From: Muchun Song <songmuchun@bytedance.com>

    commit 1685bde6b9af55923180a76152036c7fb7176db0 upstream.

    We use a global percpu int_active_memcg variable to store the remote memcg
    when we are in the interrupt context. But get_active_memcg always return
    the current->active_memcg or root_mem_cgroup. The remote memcg (set in
    the interrupt context) is ignored. This is not what we want. So fix it.

    Link: https://lkml.kernel.org/r/20210223091101.42150-1-songmuchun@bytedance.com
    Fixes: 37d5985c003d ("mm: kmem: prepare remote memcg charging infra for interrupt contexts")
    Signed-off-by: Muchun Song <songmuchun@bytedance.com>
    Reviewed-by: Shakeel Butt <shakeelb@google.com>
    Reviewed-by: Roman Gushchin <guro@fb.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    mm/memcontrol.c | 10 +++-------
    1 file changed, 3 insertions(+), 7 deletions(-)

    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -1080,13 +1080,9 @@ static __always_inline struct mem_cgroup

    rcu_read_lock();
    memcg = active_memcg();
    - if (memcg) {
    - /* current->active_memcg must hold a ref. */
    - if (WARN_ON_ONCE(!css_tryget(&memcg->css)))
    - memcg = root_mem_cgroup;
    - else
    - memcg = current->active_memcg;
    - }
    + /* remote memcg must hold a ref. */
    + if (memcg && WARN_ON_ONCE(!css_tryget(&memcg->css)))
    + memcg = root_mem_cgroup;
    rcu_read_unlock();

    return memcg;

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