From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756968AbZBWTe1 (ORCPT ); Mon, 23 Feb 2009 14:34:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754624AbZBWTeT (ORCPT ); Mon, 23 Feb 2009 14:34:19 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:39080 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753042AbZBWTeS (ORCPT ); Mon, 23 Feb 2009 14:34:18 -0500 Date: Mon, 23 Feb 2009 20:33:51 +0100 From: Ingo Molnar To: Andrew Morton Cc: paulmck@linux.vnet.ibm.com, Nick Piggin , Vegard Nossum , stable@kernel.org, Nick Piggin , Pekka Enberg , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: fix lazy vmap purging (use-after-free error) Message-ID: <20090223193351.GA11921@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> <20090223111009.d48ff81d.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090223111009.d48ff81d.akpm@linux-foundation.org> 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 * Andrew Morton wrote: > On Mon, 23 Feb 2009 08:17:26 -0800 "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. > > Please don't use system_state. The whole thing is just bad > design. It's a global variable, breaks encapsulation, creates > interactions etc. CS-101 stuff. ok, i've removed the patch - Paul, would you mind to re-send your original flag solution, with it marked __read_mostly and with the extern declarations put into a suitable header file? Paul, incidentally, this very minute i tracked down that the patch is also causing boot lockups in -tip testing. I havent yet fully debugged it, but a question comes immediately: if there's no grace periods during bootup, wont rcu_sync() & friends just hang indefinitely? More thought is needed. Ingo