From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f197.google.com (mail-wj0-f197.google.com [209.85.210.197]) by kanga.kvack.org (Postfix) with ESMTP id 9CC4E6B0038 for ; Fri, 2 Dec 2016 08:15:30 -0500 (EST) Received: by mail-wj0-f197.google.com with SMTP id he10so4353123wjc.6 for ; Fri, 02 Dec 2016 05:15:30 -0800 (PST) Received: from mail-wm0-f67.google.com (mail-wm0-f67.google.com. [74.125.82.67]) by mx.google.com with ESMTPS id lt8si5151955wjb.107.2016.12.02.05.15.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Dec 2016 05:15:29 -0800 (PST) Received: by mail-wm0-f67.google.com with SMTP id u144so2694629wmu.0 for ; Fri, 02 Dec 2016 05:15:29 -0800 (PST) Date: Fri, 2 Dec 2016 14:15:26 +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 Message-ID: <20161202131526.GI6830@dhcp22.suse.cz> References: <20161202112951.23346-1-mgorman@techsingularity.net> <20161202112951.23346-2-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161202112951.23346-2-mgorman@techsingularity.net> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , Christoph Lameter , Vlastimil Babka , Johannes Weiner , Jesper Dangaard Brouer , Joonsoo Kim , Linux-MM , Linux-Kernel On Fri 02-12-16 11:29:50, 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+] Thanks for adding the comment it should really make the code more clear. Acked-by: Michal Hocko > --- > 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 > -- > 2.10.2 > -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org