linux-kernel - Re: [PATCH] Fix check after use in kernel/exit.c

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Message-Id: <20080308.165821.119846418.xiyou.wangcong@gmail.com>
Date:	Sat, 08 Mar 2008 16:58:21 +0800 (CST)
From:	WANG Cong <xiyou.wangcong@...il.com>
To:	mingo@...e.hu
Cc:	linux-kernel@...r.kernel.org, gvaughan@....nasa.gov, akpm@...l.org,
	jeremy@...p.org
Subject: Re: [PATCH] Fix check after use in kernel/exit.c

From: Ingo Molnar <mingo@...e.hu>
Date: Sat, 8 Mar 2008 09:53:22 +0100

> 
> * Ingo Molnar <mingo@...e.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!
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