linux-kernel - Re: [PATCH 02/24] migrate: page could be locked by hwpoison, dont BUG()

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Date:	Wed, 2 Dec 2009 08:50:10 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/24] migrate: page could be locked by hwpoison, dont
 BUG()

On Wed, 2 Dec 2009, Wu Fengguang wrote:

>  mm/migrate.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- linux-mm.orig/mm/migrate.c	2009-11-02 10:18:45.000000000 +0800
> +++ linux-mm/mm/migrate.c	2009-11-02 10:26:16.000000000 +0800
> @@ -556,7 +556,7 @@ static int move_to_new_page(struct page
>  	 * holding a reference to the new page at this point.
>  	 */
>  	if (!trylock_page(newpage))
> -		BUG();
> +		return -EAGAIN;		/* got by hwpoison */
>
>  	/* Prepare mapping for the new page.*/
>  	newpage->index = page->index;

The error handling code in umap_and_move() assumes that the page is
locked upon return from move_to_new_page() even if it failed.

If you return EAGAIN then it may try to unlock a page that is not
locked.


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