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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: "Arkadiusz Miśkiewicz" <a.miskiewicz@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>
Cc: Tejun Heo <tj@kernel.org>,
	cgroups@vger.kernel.org, Aleksa Sarai <asarai@suse.de>,
	Jay Kamat <jgkamat@fb.com>, Roman Gushchin <guro@fb.com>,
	Michal Hocko <mhocko@suse.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 v2] oom, oom_reaper: do not enqueue same task twice
Date: Sat, 26 Jan 2019 22:10:52 +0900
Message-ID: <1d161137-55a5-126f-b47e-b2625bd798ca@i-love.sakura.ne.jp> (raw)
In-Reply-To: <2b0c7d6c-c58a-da7d-6f0a-4900694ec2d3@gmail.com>

On 2019/01/26 20:29, Arkadiusz Miśkiewicz wrote:
> On 26/01/2019 12:09, Tetsuo Handa wrote:
>> Arkadiusz, will you try this patch?
> 
> 
> Works. Several tries and always getting 0 pids.current after ~1s.
> 

Thank you for testing.

I updated this patch to use tsk->signal->oom_mm (a snapshot of
tsk->mm saved by mark_oom_victim(tsk)) rather than raw tsk->mm
so that we don't need to worry about possibility of changing
tsk->mm across multiple wake_oom_reaper(tsk) calls.



From 9c9e935fc038342c48461aabca666f1b544e32b1 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 26 Jan 2019 21:57:25 +0900
Subject: [PATCH v2] 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")
---
 mm/oom_kill.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f0e8cd9..057bfee 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -505,14 +505,6 @@ bool __oom_reap_task_mm(struct mm_struct *mm)
 	struct vm_area_struct *vma;
 	bool ret = true;
 
-	/*
-	 * Tell all users of get_user/copy_from_user etc... that the content
-	 * is no longer stable. No barriers really needed because unmapping
-	 * should imply barriers already and the reader would hit a page fault
-	 * if it stumbled over a reaped memory.
-	 */
-	set_bit(MMF_UNSTABLE, &mm->flags);
-
 	for (vma = mm->mmap ; vma; vma = vma->vm_next) {
 		if (!can_madv_dontneed_vma(vma))
 			continue;
@@ -647,8 +639,13 @@ 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)
+	/*
+	 * Tell all users of get_user/copy_from_user etc... that the content
+	 * is no longer stable. No barriers really needed because unmapping
+	 * should imply barriers already and the reader would hit a page fault
+	 * if it stumbled over a reaped memory.
+	 */
+	if (test_and_set_bit(MMF_UNSTABLE, &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                         ` Tetsuo Handa [this message]
2019-01-27  8:37                           ` [PATCH v2] oom, oom_reaper: do not enqueue same task twice 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
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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