On 2019/02/04 14:56, gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

This is a patch for 4.9-stable tree.

From 5e06270fbcf340dd7bda7147f4e70b81aea30f41 Mon Sep 17 00:00:00 2001

From: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Date: Mon, 4 Feb 2019 19:52:51 +0900 Subject: [PATCH] oom, oom_reaper: do not enqueue same task twice

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.... Link: http://lkml.kernel.org/r/5ee34fc6-1485-34f8-8790-903ddabaa809@i-love.sakura.... 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 --- include/linux/sched.h | 1 + mm/oom_kill.c | 4 ++-- 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h index f4a551a..ebd0afb 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -527,6 +527,7 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_OOM_SKIP 21 /* mm is of no interest for the OOM killer */ #define MMF_UNSTABLE 22 /* mm is unstable for copy_from_user */ #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */ +#define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */

#define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 4a18415..8d2be4f 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -626,8 +626,8 @@ static void wake_oom_reaper(struct task_struct *tsk) 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);