linux-kernel - Re: [PATCH] mm,migration: Avoid race between shift_arg_pages() and rmap_walk() during migration by not migrating temporary stacks

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Message-Id: <20100512135846.4fb04190.akpm@linux-foundation.org>
Date:	Wed, 12 May 2010 13:58:46 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] mm,migration: Avoid race between shift_arg_pages() and
 rmap_walk() during migration by not migrating temporary stacks

On Wed, 12 May 2010 21:51:50 +0100
Mel Gorman <mel@....ul.ie> wrote:

> On Wed, May 12, 2010 at 12:54:27PM -0700, Andrew Morton wrote:
> > On Wed, 12 May 2010 09:23:44 +0900 (JST)
> > KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> > 
> > > > diff --git a/fs/exec.c b/fs/exec.c
> > > > index 725d7ef..13f8e7f 100644
> > > > --- a/fs/exec.c
> > > > +++ b/fs/exec.c
> > > > @@ -242,9 +242,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
> > > >  	 * use STACK_TOP because that can depend on attributes which aren't
> > > >  	 * configured yet.
> > > >  	 */
> > > > +	BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
> > > 
> > > Can we use BUILD_BUG_ON()? 
> > 
> > That's vastly preferable - I made that change.
> > 
> 
> I will be surprised if it works. On x86, that is
> 
> #define VM_STACK_FLAGS  (VM_GROWSDOWN | VM_STACK_DEFAULT_FLAGS | VM_ACCOUNT)
> #define VM_STACK_DEFAULT_FLAGS VM_DATA_DEFAULT_FLAGS
> #define VM_DATA_DEFAULT_FLAGS \
>         (((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0 ) | \
>          VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
> 
> so VM_STACK_FLAGS is depending on the value of current->personality
> which we don't know at build time.

argh.  So ytf is it in ALL_CAPS?

Geeze, kids these days...
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