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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>
Cc: "Arkadiusz Miśkiewicz" <a.miskiewicz@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Tejun Heo" <tj@kernel.org>,
	cgroups@vger.kernel.org, "Aleksa Sarai" <asarai@suse.de>,
	"Jay Kamat" <jgkamat@fb.com>, "Roman Gushchin" <guro@fb.com>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	linux-kernel@vger.kernel.org,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	linux-mm <linux-mm@kvack.org>
Subject: [PATCH v3] oom, oom_reaper: do not enqueue same task twice
Date: Sun, 27 Jan 2019 23:57:38 +0900
Message-ID: <e865a044-2c10-9858-f4ef-254bc71d6cc2@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20190127114021.GB18811@dhcp22.suse.cz>

On 2019/01/27 20:40, Michal Hocko wrote:
> On Sun 27-01-19 19:56:06, Tetsuo Handa wrote:
>> On 2019/01/27 17:37, Michal Hocko wrote:
>>> Thanks for the analysis and the patch. This should work, I believe but
>>> I am not really thrilled to overload the meaning of the MMF_UNSTABLE.
>>> The flag is meant to signal accessing address space is not stable and it
>>> is not aimed to synchronize oom reaper with the oom path.
>>>
>>> Can we make use mark_oom_victim directly? I didn't get to think that
>>> through right now so I might be missing something but this should
>>> prevent repeating queueing as well.
>>
>> Yes, TIF_MEMDIE would work. But you are planning to remove TIF_MEMDIE. Also,
>> TIF_MEMDIE can't avoid enqueuing many threads sharing mm_struct to the OOM
>> reaper. There is no need to enqueue many threads sharing mm_struct because
>> the OOM reaper acts on mm_struct rather than task_struct. Thus, enqueuing
>> based on per mm_struct flag sounds better, but MMF_OOM_VICTIM cannot be
>> set from wake_oom_reaper(victim) because victim's mm might be already inside
>> exit_mmap() when wake_oom_reaper(victim) is called after task_unlock(victim).
>>
>> We could reintroduce MMF_OOM_KILLED in commit 855b018325737f76
>> ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task")
>> if you don't like overloading the meaning of the MMF_UNSTABLE. But since
>> MMF_UNSTABLE is available in Linux 4.9+ kernels (which covers all LTS stable
>> versions with the OOM reaper support), we can temporarily use MMF_UNSTABLE
>> for ease of backporting.
> 
> I agree that a per-mm state is more optimal but I would rather fix the
> issue in a clear way first and only then think about an optimization on
> top. Queueing based on mark_oom_victim (whatever that uses to guarantee
> the victim is marked atomically and only once) makes sense from the
> conceptual point of view and it makes a lot of sense to start from
> there. MMF_UNSTABLE has a completely different purpose. So unless you
> see a correctness issue with that then I would rather go that way.
> 

Then, adding a per mm_struct flag is better. I don't see the difference
between reusing MMF_UNSTABLE as a flag for whether wake_oom_reaper() for
that victim's memory was already called (what you think as an overload)
and reusing TIF_MEMDIE as a flag for whether wake_oom_reaper() for that
victim thread can be called (what I think as an overload). We want to
remove TIF_MEMDIE, and we can actually remove TIF_MEMDIE if you stop
whack-a-mole "can you observe it in real workload/program?" game.
I don't see a correctness issue with TIF_MEMDIE but I don't want to go
TIF_MEMDIE way.



From 9c9e935fc038342c48461aabca666f1b544e32b1 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sun, 27 Jan 2019 23:51:37 +0900
Subject: [PATCH v3] oom, oom_reaper: do not enqueue same task twice

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,
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.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: Arkadiusz Miśkiewicz <arekm@maven.pl>
Tested-by: Arkadiusz Miśkiewicz <arekm@maven.pl>
Fixes: af8e15cc85a25315 ("oom, oom_reaper: do not enqueue task if it is on the oom_reaper_list head")
---
 include/linux/sched/coredump.h | 1 +
 mm/oom_kill.c                  | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
index ec912d0..ecdc654 100644
--- a/include/linux/sched/coredump.h
+++ b/include/linux/sched/coredump.h
@@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm_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 |\
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f0e8cd9..059e617 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -647,8 +647,8 @@ static int oom_reaper(void *unused)
 
 static void wake_oom_reaper(struct task_struct *tsk)
 {
-	/* 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);
-- 
1.8.3.1


  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <df806a77-3327-9db5-8be2-976fde1c84e5@gmail.com>
     [not found] ` <20190117122535.njcbqhlmzozdkncw@mikami>
     [not found]   ` <1d36b181-cbaf-6694-1a31-2f7f55d15675@gmail.com>
     [not found]     ` <96ef6615-a5df-30af-b4dc-417a18ca63f1@gmail.com>
2019-01-25  7:52       ` pids.current with invalid value for hours [5.0.0 rc3 git] Arkadiusz Miśkiewicz
2019-01-25 16:37         ` Tejun Heo
2019-01-25 19:47           ` Arkadiusz Miśkiewicz
2019-01-26  1:27             ` Tetsuo Handa
2019-01-26  2:41               ` Arkadiusz Miśkiewicz
2019-01-26  6:10                 ` Tetsuo Handa
2019-01-26  7:55                   ` Tetsuo Handa
2019-01-26 11:09                     ` Tetsuo Handa
2019-01-26 11:29                       ` Arkadiusz Miśkiewicz
2019-01-26 13:10                         ` [PATCH v2] oom, oom_reaper: do not enqueue same task twice Tetsuo Handa
2019-01-27  8:37                           ` Michal Hocko
2019-01-27 10:56                             ` Tetsuo Handa
2019-01-27 11:40                               ` Michal Hocko
2019-01-27 14:57                                 ` Tetsuo Handa [this message]
2019-01-27 16:58                                   ` [PATCH v3] " Michal Hocko
2019-01-27 23:00                                   ` Roman Gushchin
2019-01-28 18:15                                   ` Andrew Morton
2019-01-28 18:42                                     ` Michal Hocko
2019-01-28 21:53                                   ` Johannes Weiner
2019-01-29 10:34                                     ` Tetsuo Handa
2019-01-26  1:41             ` pids.current with invalid value for hours [5.0.0 rc3 git] Roman Gushchin
2019-01-26  2:28               ` Arkadiusz Miśkiewicz

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