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Date: Sat, 08 Mar 2008 16:58:21 +0800 (CST)
Message-Id: <20080308.165821.119846418.xiyou.wangcong@gmail.com>
To: mingo@elte.hu
Cc: linux-kernel@vger.kernel.org, gvaughan@jpl.nasa.gov, akpm@osdl.org,
       jeremy@goop.org
Subject: Re: [PATCH] Fix check after use in kernel/exit.c
From: WANG Cong <xiyou.wangcong@gmail.com>
In-Reply-To: <20080308085322.GA29628@elte.hu>
References: <20080308.161105.253167431.xiyou.wangcong@gmail.com>
	<20080308083637.GA23555@elte.hu>
	<20080308085322.GA29628@elte.hu>
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From: Ingo Molnar <mingo@elte.hu>
Date: Sat, 8 Mar 2008 09:53:22 +0100

> 
> * Ingo Molnar <mingo@elte.hu> wrote:
> 
> > > @@ -582,9 +582,9 @@ static void exit_mm(struct task_struct * tsk)
> > >  {
> > >  	struct mm_struct *mm = tsk->mm;
> > >  
> > > -	mm_release(tsk, mm);
> > >  	if (!mm)
> > >  		return;
> > > +	mm_release(tsk, mm);
> > 
> > thanks, applied. I'm wondering why this never seems to hit in 
> > practice.
> 
> actually, i unapplied it again because the patch is wrong: mm_release() 
> has side-effects for kernel threads such as the deactivate_mm() [which 
> is important even if the user-mm is NULL]. If the NULL mm dereference 
> can really trigger then it should be avoided within mm_release().
> 

Do you mean that the NULL check should be moved into mm_release()?

Thanks!