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    Subject[PATCH tip/core/urgent 08/10] memcg: css_id() must be called under rcu_read_lock()
    Date
    This patch fixes task_in_mem_cgroup(), mem_cgroup_uncharge_swapcache(),
    mem_cgroup_move_swap_account(), and is_target_pte_for_mc() to protect
    calls to css_id(). An additional RCU lockdep splat was reported for
    memcg_oom_wake_function(), however, this function is not yet in
    mainline as of 2.6.34-rc5.

    Reported-by: Li Zefan <lizf@cn.fujitsu.com>
    Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
    Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Tested-by: Li Zefan <lizf@cn.fujitsu.com>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    ---
    mm/memcontrol.c | 21 ++++++++++++++++-----
    1 files changed, 16 insertions(+), 5 deletions(-)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index f4ede99..e06490d 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -811,10 +811,12 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
    * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
    * hierarchy(even if use_hierarchy is disabled in "mem").
    */
    + rcu_read_lock();
    if (mem->use_hierarchy)
    ret = css_is_ancestor(&curr->css, &mem->css);
    else
    ret = (curr == mem);
    + rcu_read_unlock();
    css_put(&curr->css);
    return ret;
    }
    @@ -2312,7 +2314,9 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)

    /* record memcg information */
    if (do_swap_account && swapout && memcg) {
    + rcu_read_lock();
    swap_cgroup_record(ent, css_id(&memcg->css));
    + rcu_read_unlock();
    mem_cgroup_get(memcg);
    }
    if (swapout && memcg)
    @@ -2369,8 +2373,10 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
    {
    unsigned short old_id, new_id;

    + rcu_read_lock();
    old_id = css_id(&from->css);
    new_id = css_id(&to->css);
    + rcu_read_unlock();

    if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
    mem_cgroup_swap_statistics(from, false);
    @@ -4038,11 +4044,16 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
    put_page(page);
    }
    /* throught */
    - if (ent.val && do_swap_account && !ret &&
    - css_id(&mc.from->css) == lookup_swap_cgroup(ent)) {
    - ret = MC_TARGET_SWAP;
    - if (target)
    - target->ent = ent;
    + if (ent.val && do_swap_account && !ret) {
    + unsigned short id;
    + rcu_read_lock();
    + id = css_id(&mc.from->css);
    + rcu_read_unlock();
    + if (id == lookup_swap_cgroup(ent)) {
    + ret = MC_TARGET_SWAP;
    + if (target)
    + target->ent = ent;
    + }
    }
    return ret;
    }
    --
    1.7.0


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