From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx103.postini.com [74.125.245.103]) by kanga.kvack.org (Postfix) with SMTP id 6E9DA6B004D for ; Thu, 12 Jan 2012 04:34:39 -0500 (EST) Received: from m3.gw.fujitsu.co.jp (unknown [10.0.50.73]) by fgwmail5.fujitsu.co.jp (Postfix) with ESMTP id EB49F3EE0BD for ; Thu, 12 Jan 2012 18:34:37 +0900 (JST) Received: from smail (m3 [127.0.0.1]) by outgoing.m3.gw.fujitsu.co.jp (Postfix) with ESMTP id D01D445DEF3 for ; Thu, 12 Jan 2012 18:34:37 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (s3.gw.fujitsu.co.jp [10.0.50.93]) by m3.gw.fujitsu.co.jp (Postfix) with ESMTP id AA69845DEED for ; Thu, 12 Jan 2012 18:34:37 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 9B4C41DB8041 for ; Thu, 12 Jan 2012 18:34:37 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.240.81.134]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 4DDAF1DB8038 for ; Thu, 12 Jan 2012 18:34:37 +0900 (JST) Date: Thu, 12 Jan 2012 18:33:23 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH] mm: Fix NULL ptr dereference in __count_immobile_pages Message-Id: <20120112183323.1bb62f4d.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20120112092314.GC1042@tiehlicka.suse.cz> References: <1326213022-11761-1-git-send-email-mhocko@suse.cz> <20120111084802.GA16466@tiehlicka.suse.cz> <20120112111702.3b7f2fa2.kamezawa.hiroyu@jp.fujitsu.com> <20120112082722.GB1042@tiehlicka.suse.cz> <20120112173536.db529713.kamezawa.hiroyu@jp.fujitsu.com> <20120112092314.GC1042@tiehlicka.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Mel Gorman , Andrea Arcangeli On Thu, 12 Jan 2012 10:23:14 +0100 Michal Hocko wrote: > On Thu 12-01-12 17:35:36, KAMEZAWA Hiroyuki wrote: > > On Thu, 12 Jan 2012 09:27:22 +0100 > > Michal Hocko wrote: > > > > > On Thu 12-01-12 11:17:02, KAMEZAWA Hiroyuki wrote: > > > > On Wed, 11 Jan 2012 09:48:02 +0100 > > > > Michal Hocko wrote: > > > > > > > > > On Tue 10-01-12 13:31:08, David Rientjes wrote: > > > > > > On Tue, 10 Jan 2012, Michal Hocko wrote: > > > > > [...] > > > > > > > mm/page_alloc.c | 11 +++++++++++ > > > > > > > 1 files changed, 11 insertions(+), 0 deletions(-) > > > > > > > > > > > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > > > > > index 2b8ba3a..485be89 100644 > > > > > > > --- a/mm/page_alloc.c > > > > > > > +++ b/mm/page_alloc.c > > > > > > > @@ -5608,6 +5608,17 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count) > > > > > > > bool is_pageblock_removable_nolock(struct page *page) > > > > > > > { > > > > > > > struct zone *zone = page_zone(page); > > > > > > > + unsigned long pfn = page_to_pfn(page); > > > > > > > + > > > > > > > > Hmm, I don't like to use page_zone() when we know the page may not be initialized. > > > > Shouldn't we add > > > > > > > > if (!node_online(page_to_nid(page)) > > > > return false; > > > > ? > > > > > > How is this different? The node won't be initialized in page flags as > > > well. > > > > > > > page_zone(page) is > > == > > static inline struct zone *page_zone(const struct page *page) > > { > > return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)]; > > } > > == > > > > Then, if the page is unitialized, > > > > &(NODE_DATA(0)->node_zones[0]) > > > > If NODE_DATA(0) is NULL, node_zones[0] is NULL just because zone array is placed > > on the top of struct pglist_data. > > > > I never think someone may change the layout but...Hmm, just a nitpick. > > please do as you like. > > Yes, fair point. See the follow up patch bellow. > > > > > But...hmm. I think we should return 'true' here for removing a section with a hole > > > > finally....(Now, false will be safe.) > > > > > > Those pages are reserved (for BIOS I guess) in this particular case so I > > > do not think it is safe to claim that the block is removable. Or am I > > > missing something? > > > > > > > We can't know it's reserved by BIOS or it's just a memory hole by the fact > > the page wasn't initialized. > > OK, so then we should return false to mark to block non removable, > right? Ok. > --- > From 04f74e6f0ebf28f61650d63f8884e8855fb21b55 Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Thu, 12 Jan 2012 10:19:04 +0100 > Subject: [PATCH] mm: __count_immobile_pages make sure the node is online > > page_zone requires to have an online node otherwise we are accessing > NULL NODE_DATA. This is not an issue at the moment because node_zones > are located at the structure beginning but this might change in the > future so better be careful about that. > > Signed-off-by: Michal Hocko > Signed-off-by: KAMEZAWA Hiroyuki > --- > mm/page_alloc.c | 11 +++++++++-- > 1 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 485be89..c6fb8ea 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5607,14 +5607,21 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count) > > bool is_pageblock_removable_nolock(struct page *page) > { > - struct zone *zone = page_zone(page); > - unsigned long pfn = page_to_pfn(page); > + struct zone *zone; > + unsigned long pfn; > > /* > * We have to be careful here because we are iterating over memory > * sections which are not zone aware so we might end up outside of > * the zone but still within the section. > + * We have to take care about the node as well. If the node is offline > + * its NODE_DATA will be NULL - see page_zone. > */ > + if (!node_online(page_to_nid(page))) > + return false; > + > + zone = page_zone(page); > + pfn = page_to_pfn(page); > if (!zone || zone->zone_start_pfn > pfn || > zone->zone_start_pfn + zone->spanned_pages <= pfn) > return false; !zone check can be removed because of node_online() check. Thanks, -Kame -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org