linux-kernel - [PATCH 2/5] oom: select_bad_process: PF_EXITING check should take ->mm into account

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Message-Id: <20100531183335.1846.A69D9226@jp.fujitsu.com>
Date:	Mon, 31 May 2010 18:35:39 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Oleg Nesterov <oleg@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Cc:	kosaki.motohiro@...fujitsu.com
Subject: [PATCH 2/5] oom: select_bad_process: PF_EXITING check should take ->mm into account

From: Oleg Nesterov <oleg@...hat.com>
Subject: oom: select_bad_process: PF_EXITING check should take ->mm into account

select_bad_process() checks PF_EXITING to detect the task which is going
to release its memory, but the logic is very wrong.

	- a single process P with the dead group leader disables
	  select_bad_process() completely, it will always return
	  ERR_PTR() while P can live forever

	- if the PF_EXITING task has already released its ->mm
	  it doesn't make sense to expect it is goiing to free
	  more memory (except task_struct/etc)

Change the code to ignore the PF_EXITING tasks without ->mm.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [rebase to latest -mm]
---
 mm/oom_kill.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 070b713..c87a6f4 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -287,7 +287,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
 		 * the process of exiting and releasing its resources.
 		 * Otherwise we could get an easy OOM deadlock.
 		 */
-		if (p->flags & PF_EXITING) {
+		if ((p->flags & PF_EXITING) && p->mm) {
 			if (p != current)
 				return ERR_PTR(-1UL);
 
-- 
1.6.5.2



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