Messages in this thread | | | Date | Fri, 2 Dec 2016 09:12:17 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH 1/2] mm, page_alloc: Keep pcp count and list contents in sync if struct page is corrupted |
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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@suse.de> > cc: stable@vger.kernel.org [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@suse.com>
> --- > 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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