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

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Message-Id: <20080506150213.AC63.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Tue, 06 May 2008 15:03:52 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	kosaki.motohiro@...fujitsu.com,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: on CONFIG_MM_OWNER=y, kernel panic is possible.

> That is not possible. If you look at where mm_update_next_owner() is called
> from, we call it from
> 
> exit_mm() and exec_mmap()
> 
> In both cases, we ensure that the task's mm has changed (to NULL and the new mm
> respectively), before we call mm_update_next_owner(), hence c->mm can never be
> equal to p->mm.

if so, following patch is needed instead.



---
 fs/exec.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: b/fs/exec.c
===================================================================
--- a/fs/exec.c 2008-05-04 22:57:09.000000000 +0900
+++ b/fs/exec.c 2008-05-06 15:40:35.000000000 +0900
@@ -735,7 +735,7 @@ static int exec_mmap(struct mm_struct *m
        tsk->active_mm = mm;
        activate_mm(active_mm, mm);
        task_unlock(tsk);
-       mm_update_next_owner(mm);
+       mm_update_next_owner(old_mm);
        arch_pick_mmap_layout(mm);
        if (old_mm) {
                up_read(&old_mm->mmap_sem);


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