Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757557AbcLBIMW (ORCPT ); Fri, 2 Dec 2016 03:12:22 -0500 Received: from mail-wj0-f194.google.com ([209.85.210.194]:36210 "EHLO mail-wj0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753298AbcLBIMU (ORCPT ); Fri, 2 Dec 2016 03:12:20 -0500 Date: Fri, 2 Dec 2016 09:12:17 +0100 From: Michal Hocko To: Mel Gorman Cc: Andrew Morton , Christoph Lameter , Vlastimil Babka , Johannes Weiner , Jesper Dangaard Brouer , Linux-MM , Linux-Kernel Subject: Re: [PATCH 1/2] mm, page_alloc: Keep pcp count and list contents in sync if struct page is corrupted Message-ID: <20161202081216.GA6830@dhcp22.suse.cz> References: <20161202002244.18453-1-mgorman@techsingularity.net> <20161202002244.18453-2-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161202002244.18453-2-mgorman@techsingularity.net> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2081 Lines: 63 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 > 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 > --- > 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