linux-kernel - Re: [patch 2/2] mm: remove task assumptions from swap token

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Message-Id: <20090617110034.db01479b.minchan.kim@barrios-desktop>
Date:	Wed, 17 Jun 2009 11:00:34 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Izik Eidus <ieidus@...hat.com>, Rik van Riel <riel@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] mm: remove task assumptions from swap token

Hi, Hannes. 

How about adding Hugh's comment ?

I think that is more straightforward and easy.
And it explained even real example like KSM. 

So I suggest following as.. 

==
grab_swap_token() should not make any assumptions about the running
process as the swap token is an attribute of the address space and the
faulting mm is not necessarily current->mm.

If a kthread happens to use get_user_pages() on an mm (as KSM does),
there's a chance that it will end up trying to read in a swap page,
then oops in grab_swap_token() because the kthread has no mm: GUP
passes down the right mm, so grab_swap_token() ought to be using it.
==

Anyway, It looks good to me. 
It might be just nitpick :)
If you feel it, ignore me. 
Anyway I am OK. 

On Tue, 16 Jun 2009 23:50:37 +0200
Johannes Weiner <hannes@...xchg.org> wrote:

> From: Hugh Dickins <hugh.dickins@...cali.co.uk>
> 
> grab_swap_token() should not make any assumptions about the running
> process as the swap token is an attribute of the address space and the
> faulting mm is not necessarily current->mm.
> 
> This fixes get_user_pages() from kernel threads which would blow up
> when encountering a swapped out page and grab_swap_token()
> dereferencing the unset for kernel threads current->mm.
> 
> Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Reviewed-by: Minchan Kim <minchan.kim@...il.com>

-- 
Kinds Regards
Minchan Kim
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