From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753947AbZBWRVS (ORCPT ); Mon, 23 Feb 2009 12:21:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751277AbZBWRVF (ORCPT ); Mon, 23 Feb 2009 12:21:05 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:36227 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751274AbZBWRVE (ORCPT ); Mon, 23 Feb 2009 12:21:04 -0500 Date: Mon, 23 Feb 2009 18:20:44 +0100 From: Ingo Molnar To: "Paul E. McKenney" Cc: Nick Piggin , Vegard Nossum , stable@kernel.org, Andrew Morton , Nick Piggin , Pekka Enberg , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: fix lazy vmap purging (use-after-free error) Message-ID: <20090223172044.GA29344@elte.hu> References: <20090220140157.GA12799@elte.hu> <20090222030030.GD6860@linux.vnet.ibm.com> <20090223051709.GA5990@linux.vnet.ibm.com> <200902240029.37815.nickpiggin@yahoo.com.au> <20090223161726.GD6751@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090223161726.GD6751@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul E. McKenney wrote: > On Tue, Feb 24, 2009 at 12:29:36AM +1100, Nick Piggin wrote: > > On Monday 23 February 2009 16:17:09 Paul E. McKenney wrote: > > > > > The boot CPU runs in the context of its idle thread during boot-up. > > > During this time, idle_cpu(0) will always return nonzero, which will > > > fool Classic and Hierarchical RCU into deciding that a large chunk of > > > the boot-up sequence is a big long quiescent state. This in turn causes > > > RCU to prematurely end grace periods during this time. > > > > > > This patch creates a new global variable that is set to 1 just before > > > the boot CPU first enters the scheduler, after which the idle task > > > really is idle. > > > > Nice work all (btw. if this patch goes in rather than using system_state, > > then please make the variable __read_mostly). > > Hmmm... I misread this and made system_state be > __read_mostly. Let me know if this is bad, easy to fix if > needed. no, it's the right thing to do. I'd not be surprised if we were already running into it as a performance problem - a number of common things check this flag. Ingo