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

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Date:	Tue, 06 May 2008 15:18:35 +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.

and, one more.

comment of owner member of mm_struct is bogus.
that is not guranteed point to thread-group-leader.


Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

---
 include/linux/mm_types.h |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Index: b/include/linux/mm_types.h
===================================================================
--- a/include/linux/mm_types.h  2008-05-04 22:56:52.000000000 +0900
+++ b/include/linux/mm_types.h  2008-05-06 15:53:04.000000000 +0900
@@ -231,8 +231,7 @@ struct mm_struct {
        rwlock_t                ioctx_list_lock;        /* aio lock */
        struct kioctx           *ioctx_list;
 #ifdef CONFIG_MM_OWNER
-       struct task_struct *owner;      /* The thread group leader that */
-                                       /* owns the mm_struct.          */
+       struct task_struct *owner;      /* point to one of task that owns the mm_struct. */
 #endif

 #ifdef CONFIG_PROC_FS



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