Re: [patch v2] mm, page_alloc: make first_page visible beforePageTail

[Michal Hocko]

On Tue 04-02-14 16:22:53, David Rientjes wrote:
> Commit bf6bddf1924e ("mm: introduce compaction and migration for ballooned
> pages") introduces page_count(page) into memory compaction which
> dereferences page->first_page if PageTail(page).
> 
> Introduce a store memory barrier to ensure page->first_page is properly
> initialized so that code that does page_count(page) on pages off the lru
> always have a valid p->first_page.
> 
> Reported-by: Holger Kiehl <Holger.Kiehl@xxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
>  v2: with commentary, per checkpatch
> 
>  mm/page_alloc.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -369,9 +369,11 @@ void prep_compound_page(struct page *page, unsigned long order)
>  	__SetPageHead(page);
>  	for (i = 1; i < nr_pages; i++) {
>  		struct page *p = page + i;
> -		__SetPageTail(p);
>  		set_page_count(p, 0);
>  		p->first_page = page;
> +		/* Make sure p->first_page is always valid for PageTail() */
> +		smp_wmb();
> +		__SetPageTail(p);

Where is the pairing smp_rmb? I would expect it in comound_head.

>  	}
>  }
>  

-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/