linux-kernel - [PATCH 9/9] oom: multi threaded process coredump don't make deadlock

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Message-Id: <20100617104953.FB98.A69D9226@jp.fujitsu.com>
Date:	Thu, 17 Jun 2010 10:51:44 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com
Subject: [PATCH 9/9] oom: multi threaded process coredump don't make deadlock


Oleg pointed out current PF_EXITING check is wrong. Because PF_EXITING
is per-thread flag, not per-process flag. He said,

   Two threads, group-leader L and its sub-thread T. T dumps the code.
   In this case both threads have ->mm != NULL, L has PF_EXITING.

   The first problem is, select_bad_process() always return -1 in this
   case (even if the caller is T, this doesn't matter).

   The second problem is that we should add TIF_MEMDIE to T, not L.

I think we can remove this dubious PF_EXITING check. but as first step,
This patch add the protection of multi threaded issue.

Cc: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
---
 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 b2ea2d8..4abc5c1 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -353,7 +353,7 @@ 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) && p->mm) {
+		if (thread_group_empty(p) && (p->flags & PF_EXITING) && p->mm) {
 			if (p != current)
 				return ERR_PTR(-1UL);
 
-- 
1.6.5.2



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