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From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
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: Re: [PATCH v2] oom, oom_reaper: do not enqueue same task twice
Date: Sun, 27 Jan 2019 09:37:24 +0100
Message-ID: <20190127083724.GA18811@dhcp22.suse.cz> (raw)
In-Reply-To: <1d161137-55a5-126f-b47e-b2625bd798ca@i-love.sakura.ne.jp>

On Sat 26-01-19 22:10:52, Tetsuo Handa wrote:
[...]
> >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.

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.

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f0e8cd9edb1a..dac4f2197e53 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -690,7 +690,7 @@ static void mark_oom_victim(struct task_struct *tsk)
 	WARN_ON(oom_killer_disabled);
 	/* OOM killer might race with memcg OOM */
 	if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
-		return;
+		return false;
 
 	/* oom_mm is bound to the signal struct life time. */
 	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
@@ -707,6 +707,8 @@ static void mark_oom_victim(struct task_struct *tsk)
 	__thaw_task(tsk);
 	atomic_inc(&oom_victims);
 	trace_mark_victim(tsk->pid);
+
+	return true;
 }
 
 /**
@@ -873,7 +875,7 @@ static void __oom_kill_process(struct task_struct *victim)
 	 * reserves from the user space under its control.
 	 */
 	do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID);
-	mark_oom_victim(victim);
+	can_oom_reap = mark_oom_victim(victim);
 	pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
 		task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
 		K(get_mm_counter(victim->mm, MM_ANONPAGES)),
@@ -954,8 +956,8 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 	 */
 	task_lock(p);
 	if (task_will_free_mem(p)) {
-		mark_oom_victim(p);
-		wake_oom_reaper(p);
+		if (mark_oom_victim(p)
+			wake_oom_reaper(p);
 		task_unlock(p);
 		put_task_struct(p);
 		return;
@@ -1084,8 +1086,8 @@ bool out_of_memory(struct oom_control *oc)
 	 * quickly exit and free its memory.
 	 */
 	if (task_will_free_mem(current)) {
-		mark_oom_victim(current);
-		wake_oom_reaper(current);
+		if (mark_oom_victim(current))
+			wake_oom_reaper(current);
 		return true;
 	}
 
-- 
Michal Hocko
SUSE Labs

  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 [this message]
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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