linux-kernel - on CONFIG_MM_OWNER=y, kernel panic is possible.

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Message-Id: <20080506142255.AC5D.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Tue, 06 May 2008 14:40:39 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com
Subject: on CONFIG_MM_OWNER=y, kernel panic is possible.

on CONFIG_MM_OWNER=y (that is automatically turned on by mem-cgroup),
kernel panic is possible by following scenario in mm_update_next_owner().

1. mm_update_next_owner() is called.
2. found caller task in do_each_thread() loop.
3. thus, BUG_ON(c == p) is true, it become kernel panic.

end up, We should left out current task.


Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC: Lee Schermerhorn <Lee.Schermerhorn@...com>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC: Balbir Singh <balbir@...ux.vnet.ibm.com>

---
 kernel/exit.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: b/kernel/exit.c
===================================================================
--- a/kernel/exit.c     2008-05-04 22:57:23.000000000 +0900
+++ b/kernel/exit.c     2008-05-06 15:01:26.000000000 +0900
@@ -627,7 +627,7 @@ retry:
         * here often
         */
        do_each_thread(g, c) {
-               if (c->mm == mm)
+               if ((c != p) && (c->mm == mm))
                        goto assign_new_owner;
        } while_each_thread(g, c);


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