Re: [PATCH v2] rmap: fix theoretical race between do_wp_page and shrink_active_list
From: Vladimir Davydov
Date: Wed May 13 2015 - 04:08:51 EST
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.
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