Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759599AbcLBLxk (ORCPT ); Fri, 2 Dec 2016 06:53:40 -0500 Received: from mx2.suse.de ([195.135.220.15]:55881 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757433AbcLBLxi (ORCPT ); Fri, 2 Dec 2016 06:53:38 -0500 Subject: Re: [PATCH 1/2] mm, page_alloc: Keep pcp count and list contents in sync if struct page is corrupted To: Mel Gorman , Andrew Morton References: <20161202112951.23346-1-mgorman@techsingularity.net> <20161202112951.23346-2-mgorman@techsingularity.net> Cc: Christoph Lameter , Michal Hocko , Johannes Weiner , Jesper Dangaard Brouer , Joonsoo Kim , Linux-MM , Linux-Kernel From: Vlastimil Babka Message-ID: <0a5ccb09-6f51-ca65-3c19-4c6371dbb9ba@suse.cz> Date: Fri, 2 Dec 2016 12:53:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.0 MIME-Version: 1.0 In-Reply-To: <20161202112951.23346-2-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2425 Lines: 69 On 12/02/2016 12:29 PM, 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. > > The consequence is an infinite loop if the per-cpu lists get fully drained > by free_pcppages_bulk because all the lists are empty but the count is > positive. The infinite loop occurs here > > do { > batch_free++; > if (++migratetype == MIGRATE_PCPTYPES) > migratetype = 0; > list = &pcp->lists[migratetype]; > } while (list_empty(list)); > > From a user perspective, it's a bad page warning followed by a soft lockup > with interrupts disabled in free_pcppages_bulk(). > > 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+] Acked-by: Vlastimil Babka > --- > mm/page_alloc.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 6de9440e3ae2..34ada718ef47 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 +2217,21 @@ 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)); > } > + > + /* > + * i pages were removed from the buddy list even if some leak due > + * to check_pcp_refill failing so adjust NR_FREE_PAGES based > + * on i. Do not confuse with 'alloced' which is the number of > + * pages added to the pcp list. > + */ > __mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order)); > spin_unlock(&zone->lock); > - return i; > + return alloced; > } > > #ifdef CONFIG_NUMA >