From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756019AbZCFR1S (ORCPT ); Fri, 6 Mar 2009 12:27:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753070AbZCFR1D (ORCPT ); Fri, 6 Mar 2009 12:27:03 -0500 Received: from e33.co.us.ibm.com ([32.97.110.151]:51569 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752151AbZCFR1B (ORCPT ); Fri, 6 Mar 2009 12:27:01 -0500 Subject: Re: Regression - locking (all from 2.6.28) From: Dave Hansen To: Catalin Marinas Cc: Andrew Morton , jan sonnek , linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, Peter Zijlstra , Andy Whitcroft In-Reply-To: <1236359888.3882.77.camel@pc1117.cambridge.arm.com> References: <49AC334A.9030800@gmail.com> <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> Content-Type: text/plain Date: Fri, 06 Mar 2009 09:26:55 -0800 Message-Id: <1236360415.10626.67.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2009-03-06 at 17:18 +0000, Catalin Marinas wrote: > > > Are the pgdat->node_start_pfn and pgdat->node_spanned_pages always > > > valid? Thanks. > > > > The variables themselves? I'm sure there's a window in early boot where > > they aren't valid, but other than that they should be OK unless you're > > int the middle of a hotplug operation. > > > > See pgdat_resize_(un)lock() in include/linux/memory_hotplug.h. > > I wouldn't hold a lock for that long. It's not really critical to scan > all the page structures at a time as there are subsequent scans as well, > so some can be missed. 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? -- Dave