From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx126.postini.com [74.125.245.126]) by kanga.kvack.org (Postfix) with SMTP id 2D7046B005A for ; Thu, 6 Sep 2012 03:28:47 -0400 (EDT) Date: Thu, 6 Sep 2012 16:30:20 +0900 From: Minchan Kim Subject: Re: [PATCH v2 3/3] memory-hotplug: bug fix race between isolation and allocation Message-ID: <20120906073020.GB16231@bbox> References: <1346908619-16056-1-git-send-email-minchan@kernel.org> <1346908619-16056-4-git-send-email-minchan@kernel.org> <50484E22.5010304@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50484E22.5010304@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org List-ID: To: Yasuaki Ishimatsu Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Kamezawa Hiroyuki , Xishi Qiu , Wen Congyang Hello Yasuaki, On Thu, Sep 06, 2012 at 04:17:54PM +0900, Yasuaki Ishimatsu wrote: > Hi Minchan, > > 2012/09/06 14:16, 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)); > > > > This patch checks page's migratetype in freelist in __test_page_isolated_in_pageblock. > > So now __test_page_isolated_in_pageblock can check the page caused by above race and > > can fail of memory offlining. > > > > Signed-off-by: Minchan Kim > > --- > > 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 87a7929..7ba7405 100644 > > --- a/mm/page_isolation.c > > +++ b/mm/page_isolation.c > > @@ -193,8 +193,11 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn) > > continue; > > } > > page = pfn_to_page(pfn); > > - if (PageBuddy(page)) > > + if (PageBuddy(page)) { > > + if (get_freepage_migratetype(page) != MIGRATE_ISOLATE) > > + break; > > pfn += 1 << page_order(page); > > + } > > > else if (page_count(page) == 0 && > > get_freepage_migratetype(page) == MIGRATE_ISOLATE) > > When do the if statement, the page may be used by someone. I can't understand your point. We already hold zone->lock so that allocator and this function should be atomic when the page is in free_list. If I miss something, could you elaborate it more? > In this case, page->index may have some number. If the number is same as > MIGRATE_ISOLATE, the code goes worng. > > Thanks, > Yasuaki Ishimatsu > > > pfn += 1; > > > > > -- > 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