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From: Johannes Weiner <hannes@cmpxchg.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: "Michal Hocko" <mhocko@kernel.org>,
	"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>,
	linux-kernel@vger.kernel.org,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH v3] oom, oom_reaper: do not enqueue same task twice
Date: Mon, 28 Jan 2019 16:53:15 -0500
Message-ID: <20190128215315.GA2011@cmpxchg.org> (raw)
In-Reply-To: <e865a044-2c10-9858-f4ef-254bc71d6cc2@i-love.sakura.ne.jp>

Hi Tetsuo,

On Sun, Jan 27, 2019 at 11:57:38PM +0900, Tetsuo Handa wrote:
> 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.

This changelog seems a little terse compared to how tricky this is.

Can you please include an explanation here *how* this bug is possible?
I.e. the race condition that causes the function te be entered twice
and the existing re-entrance check in there to fail.

> 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.

  parent 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                                 ` [PATCH v3] " Tetsuo Handa
2019-01-27 16:58                                   ` 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 [this message]
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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