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    Subject[PATCH 4.14 39/46] oom, oom_reaper: do not enqueue same task twice
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

    commit 9bcdeb51bd7d2ae9fe65ea4d60643d2aeef5bfe3 upstream.

    Arkadiusz reported that enabling memcg's group oom killing causes
    strange memcg statistics where there is no task in a memcg despite the
    number of tasks in that memcg is not 0. It turned out that there is a
    bug in wake_oom_reaper() which allows enqueuing same task twice which
    makes impossible to decrease the number of tasks in that memcg due to a
    refcount leak.

    This bug existed since the OOM reaper became invokable from
    task_will_free_mem(current) path in out_of_memory() in Linux 4.7,

    T1@P1 |T2@P1 |T3@P1 |OOM reaper
    ----------+----------+----------+------------
    # Processing an OOM victim in a different memcg domain.
    try_charge()
    mem_cgroup_out_of_memory()
    mutex_lock(&oom_lock)
    try_charge()
    mem_cgroup_out_of_memory()
    mutex_lock(&oom_lock)
    try_charge()
    mem_cgroup_out_of_memory()
    mutex_lock(&oom_lock)
    out_of_memory()
    oom_kill_process(P1)
    do_send_sig_info(SIGKILL, @P1)
    mark_oom_victim(T1@P1)
    wake_oom_reaper(T1@P1) # T1@P1 is enqueued.
    mutex_unlock(&oom_lock)
    out_of_memory()
    mark_oom_victim(T2@P1)
    wake_oom_reaper(T2@P1) # T2@P1 is enqueued.
    mutex_unlock(&oom_lock)
    out_of_memory()
    mark_oom_victim(T1@P1)
    wake_oom_reaper(T1@P1) # T1@P1 is enqueued again due to oom_reaper_list == T2@P1 && T1@P1->oom_reaper_list == NULL.
    mutex_unlock(&oom_lock)
    # Completed processing an OOM victim in a different memcg domain.
    spin_lock(&oom_reaper_lock)
    # T1P1 is dequeued.
    spin_unlock(&oom_reaper_lock)

    but memcg's group oom killing made it easier to trigger this bug by
    calling wake_oom_reaper() on the same task from one out_of_memory()
    request.

    Fix this bug using an approach used by commit 855b018325737f76 ("oom,
    oom_reaper: disable oom_reaper for oom_kill_allocating_task"). As a
    side effect of this patch, this patch also avoids enqueuing multiple
    threads sharing memory via task_will_free_mem(current) path.

    Link: http://lkml.kernel.org/r/e865a044-2c10-9858-f4ef-254bc71d6cc2@i-love.sakura.ne.jp
    Link: http://lkml.kernel.org/r/5ee34fc6-1485-34f8-8790-903ddabaa809@i-love.sakura.ne.jp
    Fixes: af8e15cc85a25315 ("oom, oom_reaper: do not enqueue task if it is on the oom_reaper_list head")
    Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Reported-by: Arkadiusz Miskiewicz <arekm@maven.pl>
    Tested-by: Arkadiusz Miskiewicz <arekm@maven.pl>
    Acked-by: Michal Hocko <mhocko@suse.com>
    Acked-by: Roman Gushchin <guro@fb.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Aleksa Sarai <asarai@suse.de>
    Cc: Jay Kamat <jgkamat@fb.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    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>

    ---
    include/linux/sched/coredump.h | 1 +
    mm/oom_kill.c | 4 ++--
    2 files changed, 3 insertions(+), 2 deletions(-)

    --- a/include/linux/sched/coredump.h
    +++ b/include/linux/sched/coredump.h
    @@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm
    #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */
    #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */
    #define MMF_OOM_VICTIM 25 /* mm is the oom victim */
    +#define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */
    #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP)

    #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\
    --- a/mm/oom_kill.c
    +++ b/mm/oom_kill.c
    @@ -628,8 +628,8 @@ static void wake_oom_reaper(struct task_
    if (!oom_reaper_th)
    return;

    - /* tsk is already queued? */
    - if (tsk == oom_reaper_list || tsk->oom_reaper_list)
    + /* mm is already queued? */
    + if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
    return;

    get_task_struct(tsk);

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