linux-kernel - Re: [PATCH 6/5] oom, oom_reaper: disable oom

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Date:	Fri, 19 Feb 2016 19:34:19 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Rientjes <rientjes@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Argangeli <andrea@...nel.org>,
	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/5] oom, oom_reaper: disable oom_reaper for

On Wed 17-02-16 10:48:55, Michal Hocko wrote:
> Hi Andrew,
> although this can be folded into patch 5
> (mm-oom_reaper-implement-oom-victims-queuing.patch) I think it would be
> better to have it separate and revert after we sort out the proper
> oom_kill_allocating_task behavior or handle exclusion at oom_reaper
> level.

An alternative would be something like the following. It is definitely
less hackish but it steals one bit in mm->flags. We do not seem to be
in shortage there now but who knows. Does this sound better? Later
changes might even consider the flag for the victim selection and ignore
those which already have the flag set. But I didn't think about it more
to form a patch yet.
---
>From 8b17e66a70edac65ecd6df411a675cf3d840a9fe Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.com>
Date: Wed, 17 Feb 2016 10:40:41 +0100
Subject: [PATCH] oom, oom_reaper: disable oom_reaper for
 oom_kill_allocating_task

Tetsuo has reported that oom_kill_allocating_task=1 will cause
oom_reaper_list corruption because oom_kill_process doesn't follow
standard OOM exclusion (aka ignores TIF_MEMDIE) and allows to enqueue
the same task multiple times - e.g. by sacrificing the same child
multiple times.

This patch fixes the issue by introducing a new MMF_OOM_KILLED mm flag
which is set in oom_kill_process atomically and oom reaper is disabled
if the flag was already set.

Reported-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 include/linux/sched.h | 2 ++
 mm/oom_kill.c         | 6 +++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c25996c336de..0552cd5696c2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -509,6 +509,8 @@ static inline int get_dumpable(struct mm_struct *mm)
 #define MMF_HAS_UPROBES		19	/* has uprobes */
 #define MMF_RECALC_UPROBES	20	/* MMF_HAS_UPROBES can be wrong */
 
+#define MMF_OOM_KILLED		21	/* OOM killer has chosen this mm */
+
 #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 
 struct sighand_struct {
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 7e9953a64489..32ce05b1aa10 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -678,7 +678,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 	unsigned int victim_points = 0;
 	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
 					      DEFAULT_RATELIMIT_BURST);
-	bool can_oom_reap = true;
+	bool can_oom_reap;
 
 	/*
 	 * If the task is already exiting, don't alarm the sysadmin or kill
@@ -740,6 +740,10 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 	/* Get a reference to safely compare mm after task_unlock(victim) */
 	mm = victim->mm;
 	atomic_inc(&mm->mm_count);
+
+	/* Make sure we do not try to oom reap the mm multiple times */
+	can_oom_reap = !test_and_set_bit(MMF_OOM_KILLED, &mm->flags);
+
 	/*
 	 * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
 	 * the OOM victim from depleting the memory reserves from the user
-- 
2.7.0


-- 
Michal Hocko
SUSE Labs