On Fri 02-12-16 00:22:43, Mel Gorman wrote:
> Vlastimil Babka pointed out that commit 479f854a207c ("mm, page_alloc:
> defer debugging checks of pages allocated from the PCP") will allow the
> per-cpu list counter to be out of sync with the per-cpu list contents
> if a struct page is corrupted. This patch keeps the accounting in sync.
>
> Fixes: 479f854a207c ("mm, page_alloc: defer debugging checks of pages allocated from the PCP")
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> cc: stable@xxxxxxxxxxxxxxx [4.7+]
I am trying to think about what would happen if we did go out of sync
and cannot spot a problem. Vlastimil has mentioned something about
free_pcppages_bulk looping for ever but I cannot see it happening right
now. So why is this worth stable backport?
Anyway the patch looks correct
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/page_alloc.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6de9440e3ae2..777ed59570df 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2192,7 +2192,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
> unsigned long count, struct list_head *list,
> int migratetype, bool cold)
> {
> - int i;
> + int i, alloced = 0;
>
> spin_lock(&zone->lock);
> for (i = 0; i < count; ++i) {
> @@ -2217,13 +2217,14 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
> else
> list_add_tail(&page->lru, list);
> list = &page->lru;
> + alloced++;
> if (is_migrate_cma(get_pcppage_migratetype(page)))
> __mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
> -(1 << order));
> }
> __mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
I guess this deserves a comment (i vs. alloced is confusing and I bet
somebody will come up with a cleanup...). We leak corrupted pages
intentionally so we should uncharge them from the NR_FREE_PAGES.
> spin_unlock(&zone->lock);
> - return i;
> + return alloced;
> }
>
> #ifdef CONFIG_NUMA
> --
> 2.10.2
>
--
Michal Hocko
SUSE Labs
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