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    Subject[PATCH 5/5] memcg, tcp_kmem: check for cg_proto in sock_update_memcg
    Date
    From: Michal Hocko <mhocko@suse.cz>

    sk_prot->proto_cgroup is allowed to return NULL but sock_update_memcg
    doesn't check for NULL. The function relies on the mem_cgroup_is_root
    check because we shouldn't get NULL otherwise because
    mem_cgroup_from_task will always return !NULL.

    All other callers are checking for NULL and we can safely replace
    mem_cgroup_is_root() check by cg_proto != NULL which will be more
    straightforward (proto_cgroup returns NULL for the root memcg already).

    Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
    Signed-off-by: Michal Hocko <mhocko@suse.cz>
    ---
    mm/memcontrol.c | 3 +--
    1 file changed, 1 insertion(+), 2 deletions(-)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 5d4fba8cbdd0..cf9fb1f41831 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -315,8 +315,7 @@ void sock_update_memcg(struct sock *sk)
    rcu_read_lock();
    memcg = mem_cgroup_from_task(current);
    cg_proto = sk->sk_prot->proto_cgroup(memcg);
    - if (!mem_cgroup_is_root(memcg) &&
    - memcg_proto_active(cg_proto) &&
    + if (cg_proto && memcg_proto_active(cg_proto) &&
    css_tryget_online(&memcg->css)) {
    sk->sk_cgrp = cg_proto;
    }
    --
    2.1.4


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