From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757415Ab2GQXjk (ORCPT ); Tue, 17 Jul 2012 19:39:40 -0400 Received: from LGEMRELSE1Q.lge.com ([156.147.1.111]:65340 "EHLO LGEMRELSE1Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754751Ab2GQXjc (ORCPT ); Tue, 17 Jul 2012 19:39:32 -0400 X-AuditID: 9c93016f-b7b08ae00000790d-4a-5005f7b2055f Date: Wed, 18 Jul 2012 08:40:03 +0900 From: Minchan Kim To: Bob Liu Cc: Kamezawa Hiroyuki , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , KOSAKI Motohiro , Hugh Dickins Subject: Re: [RFC 3/3] memory-hotplug: bug fix race between isolation and allocation Message-ID: <20120717234003.GA26937@bbox> References: <1342508505-23492-1-git-send-email-minchan@kernel.org> <1342508505-23492-4-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Bob, On Tue, Jul 17, 2012 at 06:13:17PM +0800, Bob Liu wrote: > Hi Minchan, > > On Tue, Jul 17, 2012 at 3:01 PM, Minchan Kim wrote: > > Like below, memory-hotplug makes race between page-isolation > > and page-allocation so it can hit BUG_ON in __offline_isolated_pages. > > > > CPU A CPU B > > > > start_isolate_page_range > > set_migratetype_isolate > > spin_lock_irqsave(zone->lock) > > > > free_hot_cold_page(Page A) > > /* without zone->lock */ > > migratetype = get_pageblock_migratetype(Page A); > > /* > > * Page could be moved into MIGRATE_MOVABLE > > * of per_cpu_pages > > */ > > list_add_tail(&page->lru, &pcp->lists[migratetype]); > > > > set_pageblock_isolate > > move_freepages_block > > drain_all_pages > > > > /* Page A could be in MIGRATE_MOVABLE of free_list. */ > > > > check_pages_isolated > > __test_page_isolated_in_pageblock > > /* > > * We can't catch freed page which > > * is free_list[MIGRATE_MOVABLE] > > */ > > if (PageBuddy(page A)) > > pfn += 1 << page_order(page A); > > > > /* So, Page A could be allocated */ > > > > __offline_isolated_pages > > /* > > * BUG_ON hit or offline page > > * which is used by someone > > */ > > BUG_ON(!PageBuddy(page A)); > > > > Signed-off-by: Minchan Kim > > --- > > I found this problem during code review so please confirm it. > > Kame? > > > > mm/page_isolation.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > > index acf65a7..4699d1f 100644 > > --- a/mm/page_isolation.c > > +++ b/mm/page_isolation.c > > @@ -196,8 +196,11 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn) > > continue; > > } > > page = pfn_to_page(pfn); > > - if (PageBuddy(page)) > > + if (PageBuddy(page)) { > > pfn += 1 << page_order(page); > > + if (get_page_migratetype(page) != MIGRATE_ISOLATE) > > + break; > > + } > > test_page_isolated() already have check > get_pageblock_migratetype(page) != MIGRATE_ISOLATE. > That's why I send a patch. As I describe in description, pageblock migration type of get_page_migratetype(page) is inconsistent with free_list[migrationtype]. I mean get_pageblock_migratetype(page) will return MIGRATE_ISOLATE but the page would be in free_list[MIGRATE_MOVABLE] so it could be allocated for someone if that race happens. -- Kind regards, Minchan Kim