linux-kernel - Re: [PATCH] mm: pass mm to grab_swap

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Message-Id: <20090622093247.bc4f4c0f.minchan.kim@barrios-desktop>
Date:	Mon, 22 Jun 2009 09:32:47 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Izik Eidus <ieidus@...hat.com>, Rik van Riel <riel@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Minchan Kim <minchan.kim@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: pass mm to grab_swap_token

On Sun, 21 Jun 2009 14:02:43 +0100 (BST)
Hugh Dickins <hugh.dickins@...cali.co.uk> wrote:

> 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.
> 
> We have not identified a stronger case than KSM's daemon (not yet
> in mainline), but the issue must have come up before, since RHEL has
> included a fix for this for years (though a different fix, they just
> back out of grab_swap_token if current->mm is unset: which is what
> we first proposed, but using the right mm here seems more correct).
> 
> Reported-by: Izik Eidus <ieidus@...hat.com>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
> Acked-by: Rik van Riel <riel@...hat.com>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

I already added my sign to Hannes but it is folded in this patch.

-- 
Kinds Regards
Minchan Kim
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