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    Subject[PATCH 4.9 044/107] memcg: remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Kirill Tkhai <ktkhai@virtuozzo.com>

    [ Upstream commit 7e97de0b033bcac4fa9a35cef72e0c06e6a22c67 ]

    In case of memcg_online_kmem() failure, memcg_cgroup::id remains hashed
    in mem_cgroup_idr even after memcg memory is freed. This leads to leak
    of ID in mem_cgroup_idr.

    This patch adds removal into mem_cgroup_css_alloc(), which fixes the
    problem. For better readability, it adds a generic helper which is used
    in mem_cgroup_alloc() and mem_cgroup_id_put_many() as well.

    Link: http://lkml.kernel.org/r/152354470916.22460.14397070748001974638.stgit@localhost.localdomain
    Fixes 73f576c04b94 ("mm: memcontrol: fix cgroup creation failure after many small jobs")
    Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
    Acked-by: Johannes Weiner <hannes@cmpxchg.org>
    Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    mm/memcontrol.c | 15 +++++++++++----
    1 file changed, 11 insertions(+), 4 deletions(-)

    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -4072,6 +4072,14 @@ static struct cftype mem_cgroup_legacy_f

    static DEFINE_IDR(mem_cgroup_idr);

    +static void mem_cgroup_id_remove(struct mem_cgroup *memcg)
    +{
    + if (memcg->id.id > 0) {
    + idr_remove(&mem_cgroup_idr, memcg->id.id);
    + memcg->id.id = 0;
    + }
    +}
    +
    static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
    {
    VM_BUG_ON(atomic_read(&memcg->id.ref) <= 0);
    @@ -4082,8 +4090,7 @@ static void mem_cgroup_id_put_many(struc
    {
    VM_BUG_ON(atomic_read(&memcg->id.ref) < n);
    if (atomic_sub_and_test(n, &memcg->id.ref)) {
    - idr_remove(&mem_cgroup_idr, memcg->id.id);
    - memcg->id.id = 0;
    + mem_cgroup_id_remove(memcg);

    /* Memcg ID pins CSS */
    css_put(&memcg->css);
    @@ -4208,8 +4215,7 @@ static struct mem_cgroup *mem_cgroup_all
    idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
    return memcg;
    fail:
    - if (memcg->id.id > 0)
    - idr_remove(&mem_cgroup_idr, memcg->id.id);
    + mem_cgroup_id_remove(memcg);
    __mem_cgroup_free(memcg);
    return NULL;
    }
    @@ -4268,6 +4274,7 @@ mem_cgroup_css_alloc(struct cgroup_subsy

    return &memcg->css;
    fail:
    + mem_cgroup_id_remove(memcg);
    mem_cgroup_free(memcg);
    return ERR_PTR(-ENOMEM);
    }

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