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

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Message-ID: <20080308085322.GA29628@elte.hu>
Date:	Sat, 8 Mar 2008 09:53:22 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	WANG Cong <xiyou.wangcong@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"G. Vaughan" <gvaughan@....nasa.gov>,
	Andrew Morton <akpm@...l.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH] Fix check after use in kernel/exit.c


* 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().

	Ingo
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