From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx162.postini.com [74.125.245.162]) by kanga.kvack.org (Postfix) with SMTP id 7C4C46B004D for ; Thu, 12 Jan 2012 04:23:19 -0500 (EST) Date: Thu, 12 Jan 2012 10:23:14 +0100 From: Michal Hocko Subject: Re: [PATCH] mm: Fix NULL ptr dereference in __count_immobile_pages Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120112173536.db529713.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Mel Gorman , Andrea Arcangeli 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? ---