From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756206Ab0IGJbJ (ORCPT ); Tue, 7 Sep 2010 05:31:09 -0400 Received: from gir.skynet.ie ([193.1.99.77]:44001 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756194Ab0IGJa7 (ORCPT ); Tue, 7 Sep 2010 05:30:59 -0400 Date: Tue, 7 Sep 2010 10:30:44 +0100 From: Mel Gorman To: Hiroyuki Kamezawa Cc: KAMEZAWA Hiroyuki , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Michal Hocko , fengguang.wu@intel.com, "akpm@linux-foundation.org" , andi.kleen@intel.com, Dave Hansen , stable@kernel.org Subject: Re: [BUGFIX][PATCH 1/3] memory hotplug: fix next block calculation in is_removable Message-ID: <20100907093044.GR8384@csn.ul.ie> References: <20100906144019.946d3c49.kamezawa.hiroyu@jp.fujitsu.com> <20100906144228.4ee5a738.kamezawa.hiroyu@jp.fujitsu.com> <20100906133914.GL8384@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 07, 2010 at 02:15:01AM +0900, Hiroyuki Kamezawa wrote: > 2010/9/6 Mel Gorman : > > On Mon, Sep 06, 2010 at 02:42:28PM +0900, KAMEZAWA Hiroyuki wrote: > >> > >> From: KAMEZAWA Hiroyuki > >> > >> next_active_pageblock() is for finding next _used_ freeblock. It skips > >> several blocks when it finds there are a chunk of free pages lager than > >> pageblock. But it has 2 bugs. > >> > >>   1. We have no lock. page_order(page) - pageblock_order can be minus. > >>   2. pageblocks_stride += is wrong. it should skip page_order(p) of pages. > >> > >> CC: stable@kernel.org > >> Signed-off-by: KAMEZAWA Hiroyuki > >> --- > >>  mm/memory_hotplug.c |   16 ++++++++-------- > >>  1 file changed, 8 insertions(+), 8 deletions(-) > >> > >> Index: kametest/mm/memory_hotplug.c > >> =================================================================== > >> --- kametest.orig/mm/memory_hotplug.c > >> +++ kametest/mm/memory_hotplug.c > >> @@ -584,19 +584,19 @@ static inline int pageblock_free(struct > >>  /* Return the start of the next active pageblock after a given page */ > >>  static struct page *next_active_pageblock(struct page *page) > >>  { > >> -     int pageblocks_stride; > >> - > >>       /* Ensure the starting page is pageblock-aligned */ > >>       BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1)); > >> > >> -     /* Move forward by at least 1 * pageblock_nr_pages */ > >> -     pageblocks_stride = 1; > >> - > >>       /* If the entire pageblock is free, move to the end of free page */ > >> -     if (pageblock_free(page)) > >> -             pageblocks_stride += page_order(page) - pageblock_order; > >> +     if (pageblock_free(page)) { > >> +             int order; > >> +             /* be careful. we don't have locks, page_order can be changed.*/ > >> +             order = page_order(page); > >> +             if (order > pageblock_order) > >> +                     return page + (1 << order); > >> +     } > > > > As you note in your changelog, page_order() is unsafe because we do not have > > the zone lock but you don't check if order is somewhere between pageblock_order > > and MAX_ORDER_NR_PAGES. How is this safer? > > > Ah, I missed that. > > if ((pageblock_order <= order) && (order < MAX_ORDER)) > return page + (1 << order); > ok ? > Seems ok. There will still be some false usage of order but it should be harmless. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab