From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx160.postini.com [74.125.245.160]) by kanga.kvack.org (Postfix) with SMTP id DD4E86B005A for ; Tue, 17 Jul 2012 23:55:34 -0400 (EDT) Date: Wed, 18 Jul 2012 12:56:06 +0900 From: Minchan Kim Subject: Re: [RFC 3/3] memory-hotplug: bug fix race between isolation and allocation Message-ID: <20120718035606.GA31662@bbox> References: <1342508505-23492-1-git-send-email-minchan@kernel.org> <1342508505-23492-4-git-send-email-minchan@kernel.org> <20120717234003.GA26937@bbox> <20120718024157.GA31180@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Bob Liu Cc: Kamezawa Hiroyuki , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , KOSAKI Motohiro , Hugh Dickins On Wed, Jul 18, 2012 at 11:12:27AM +0800, Bob Liu wrote: > On Wed, Jul 18, 2012 at 10:41 AM, Minchan Kim wrote: > > On Wed, Jul 18, 2012 at 10:12:57AM +0800, Bob Liu wrote: > >> On Wed, Jul 18, 2012 at 7:40 AM, Minchan Kim wrote: > >> > 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. > >> > > >> > >> Sorry, I'm still not get the situation how this race happens. > >> > >> set_pageblock_isolate > >> move_freepages_block > >> drain_all_pages > >> > >> /* Page A could be in MIGRATE_MOVABLE > >> of free_list. */ > >> > >> I think move_freepages_block() will call list_move() to move Page A to > >> free_list[MIGRATE_ISOLATE], so this case can't happen? > > > > move_freepages_block handles only pages in free_list but Page A is on pcp, not free_list. > > > > Got it, then why not just drain pcp pages before move_freepages_block() ? CPU A CPU B drain_all_pages lock(zone->lock); free_hot_cold_page MIGRATE_MOVABLE = get_pageblock_migratetype(page); list_add(&page->lru, &pcp->lists[migratetype]) set_pageblock_isolate move_free_pages_block unlock(zone->lock); We can't make it atomic. > > And I didn't see the effect by adding the check if > (get_page_migratetype(page) != MIGRATE_ISOLATE) for this race. > Since set_pageblock_isolate() have been called by CPU A, this check > will always false which cause CPU A still consider Page A isolated, > then PAGE A still can be allocated by CPU B from pcp. Please don't confuse get_page_migratetype and get_pageblock_migratetype. get_page_migratetype returns migratetype inforamtion of *page* which is in free_list while get_pageblock_migratetype returns *pageblock*'s migratetype. > > -- > Regards, > --Bob > > -- > 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 -- Kind regards, Minchan Kim -- 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