From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756316AbZCFTZt (ORCPT ); Fri, 6 Mar 2009 14:25:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753790AbZCFTZh (ORCPT ); Fri, 6 Mar 2009 14:25:37 -0500 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:48915 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755194AbZCFTZh (ORCPT ); Fri, 6 Mar 2009 14:25:37 -0500 Date: Fri, 6 Mar 2009 20:28:12 +0100 From: Pavel Machek To: Dave Hansen Cc: Catalin Marinas , Andrew Morton , jan sonnek , linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, Peter Zijlstra , Andy Whitcroft , "Rafael J. Wysocki" Subject: Re: Regression - locking (all from 2.6.28) Message-ID: <20090306192812.GA26767@elf.ucw.cz> References: <20090302121127.e46dc4be.akpm@linux-foundation.org> <1236076864.8547.20.camel@pc1117.cambridge.arm.com> <1236092480.8547.67.camel@pc1117.cambridge.arm.com> <1236214452.22399.68.camel@nimitz> <1236357616.3882.66.camel@pc1117.cambridge.arm.com> <1236358369.10626.58.camel@nimitz> <1236359888.3882.77.camel@pc1117.cambridge.arm.com> <1236360415.10626.67.camel@nimitz> <1236362436.3882.80.camel@pc1117.cambridge.arm.com> <1236367186.10626.84.camel@nimitz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1236367186.10626.84.camel@nimitz> X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html