From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756837AbZCPWEq (ORCPT ); Mon, 16 Mar 2009 18:04:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752669AbZCPWEh (ORCPT ); Mon, 16 Mar 2009 18:04:37 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:50955 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779AbZCPWEg (ORCPT ); Mon, 16 Mar 2009 18:04:36 -0400 From: "Rafael J. Wysocki" To: Pavel Machek Subject: Re: Regression - locking (all from 2.6.28) Date: Mon, 16 Mar 2009 23:04:27 +0100 User-Agent: KMail/1.11.1 (Linux/2.6.29-rc8-tst; KDE/4.2.1; x86_64; ; ) Cc: Dave Hansen , Catalin Marinas , Andrew Morton , jan sonnek , linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, Peter Zijlstra , Andy Whitcroft , KAMEZAWA Hiroyuki References: <20090302121127.e46dc4be.akpm@linux-foundation.org> <1236367186.10626.84.camel@nimitz> <20090306192812.GA26767@elf.ucw.cz> In-Reply-To: <20090306192812.GA26767@elf.ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200903162304.28944.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 06 March 2009, Pavel Machek wrote: > Hi! > > On Fri 2009-03-06 11:19:46, Dave Hansen wrote: > > On Fri, 2009-03-06 at 18:00 +0000, Catalin Marinas wrote: > > > > I think you should be more worried about consistency rather than missing > > > > entries. Take these two lines of code: > > > > > > > > start_pfn = node->node_start_pfn; > > > > /* hotplug occurs here */ > > > > end_pfn = start_pfn + node->node_spanned_pages; > > > > > > > > What if someone comes in and adds memory to the node, at the beginning > > > > of the node, after you have calculated start_pfn? Try to think of what > > > > value you'll get for end_pfn and whether it is consistent and was *ever* > > > > valid at all. Would that oops the kernel? > > > > > > I assume pfn_valid() should handle this and kmemleak wouldn't scan the > > > page, unless we need locks around pfn_valid as well but I haven't seen > > > any used in the kernel. > > > > You assume incorrectly. :( > > > > Take my above example, and assume that you have two nodes which are > > right next to each other. You might run over the end of one node and > > into the next one. Your pages will be pfn_valid() but you will be on > > the wrong node. > > > > Please take a look at those locks that I mentioned. Notice that they > > are lock the pgdat *span*, not the validity of pages inside the pgdat. > > Your code deals with what pages the pgdats *span* and thus needs that > > lock. Notice that my example also had to do with those two lines of > > code incorrectly guessing the pgdat's *span*. > > > > We recently went to some pain to make sure that the software suspend > > code (which walks pgdat ranges as well) worked with memory hotplug. > > There really isn't that much code around that actually cares at runtime > > about which physical areas a particular node or zone spans. Yours is a > > rarity and will require some caution. > > > > You could probably also use the memory hotplug mutex found here: > > > > https://lists.linux-foundation.org/pipermail/linux-pm/2008-November/018884.html > > > > But I'm not sure where those patches have gone. Hmmm. Pavel? > > I don't think they were applied. They probably should... Rafael was > about to look into that, but he lost the patch pointer. Yes. In fact, sending the patch again to me would be appreciated. Thanks, Rafael