linux-kernel - Re: [PATCH v2] rmap: fix theoretical race between do_wp_page and shrink_active

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Date:	Wed, 13 May 2015 11:08:23 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2] rmap: fix theoretical race between do_wp_page and
 shrink_active_list

On Tue, May 12, 2015 at 03:28:40PM -0700, Andrew Morton wrote:
> Please let's not put things like WRITE_ONCE() in there without
> documenting them - otherwise it's terribly hard for readers to work out
> why it was added.
> 
> How's this look?
> 
> --- a/mm/rmap.c~rmap-fix-theoretical-race-between-do_wp_page-and-shrink_active_list-fix
> +++ a/mm/rmap.c
> @@ -950,6 +950,11 @@ void page_move_anon_rmap(struct page *pa
>  	VM_BUG_ON_PAGE(page->index != linear_page_index(vma, address), page);
>  
>  	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
> +	/*
> +	 * Ensure that anon_vma and the PAGE_MAPPING_ANON bit are written
> +	 * simultaneously, so a concurrent reader (eg shrink_active_list) will
> +	 * not see one without the other.
> +	 */
>  	WRITE_ONCE(page->mapping, (struct address_space *) anon_vma);
>  }

Looks good to me.

Thanks,
Vladimir
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