From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756364AbZBWRC3 (ORCPT ); Mon, 23 Feb 2009 12:02:29 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754474AbZBWRCU (ORCPT ); Mon, 23 Feb 2009 12:02:20 -0500 Received: from e4.ny.us.ibm.com ([32.97.182.144]:49035 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754028AbZBWRCT (ORCPT ); Mon, 23 Feb 2009 12:02:19 -0500 Date: Mon, 23 Feb 2009 07:56:05 -0800 From: "Paul E. McKenney" To: Ingo Molnar Cc: Andrew Morton , 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: <20090223155605.GC6751@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090221014056.GU6960@linux.vnet.ibm.com> <19f34abd0902210130p62fba6d0n906b321949409578@mail.gmail.com> <20090221174703.GA6860@linux.vnet.ibm.com> <19f34abd0902211008k39afd449k604aaf34f693c9a6@mail.gmail.com> <19f34abd0902211037w2293af16t561444d11cc834b8@mail.gmail.com> <20090222030030.GD6860@linux.vnet.ibm.com> <20090223051709.GA5990@linux.vnet.ibm.com> <20090223090735.GH9582@elte.hu> <20090223011712.853aa94d.akpm@linux-foundation.org> <20090223092744.GL9582@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090223092744.GL9582@elte.hu> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 23, 2009 at 10:27:44AM +0100, Ingo Molnar wrote: > > * Andrew Morton wrote: > > > On Mon, 23 Feb 2009 10:07:35 +0100 Ingo Molnar wrote: > > > > > > --- > > > > > > > > init/main.c | 3 +++ > > > > kernel/rcuclassic.c | 4 +++- > > > > kernel/rcutree.c | 4 +++- > > > > 3 files changed, 9 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/init/main.c b/init/main.c > > > > index 8442094..51f4b71 100644 > > > > --- a/init/main.c > > > > +++ b/init/main.c > > > > @@ -121,6 +121,8 @@ static char *static_command_line; > > > > static char *execute_command; > > > > static char *ramdisk_execute_command; > > > > > > > > +int idle_task_is_really_idle; /* set to 1 late in boot. */ > > > > + > > > > #ifdef CONFIG_SMP > > > > /* Setup configured maximum number of CPUs to activate */ > > > > unsigned int __initdata setup_max_cpus = NR_CPUS; > > > > @@ -463,6 +465,7 @@ static noinline void __init_refok rest_init(void) > > > > * at least once to get things moving: > > > > */ > > > > init_idle_bootup_task(current); > > > > + idle_task_is_really_idle = 1; > > > > preempt_enable_no_resched(); > > > > schedule(); > > > > preempt_disable(); > > > > > > Could you please use system_state instead? We could insert a new > > > stage - or just use SYSTEM_RUNNING as the trigger. > > > > I think the standalone flag is better (once those > > extern-decls-in-C get fixed). > > > > system_state's semantics have, err, evolved over time. If > > this happens again (and the patch sneaks past my attention) > > then there's a risk that code which depends upon system_state > > will break - this has happened in the past. Plus piling more > > dependencies on system_state of course makes any evolution of > > its semantics harder to do... > > All we need is a SYSTEM_BOOTING_EARLY boundary - prior which > there's no real scheduling yet. I used SYSTEM_SCHEDULER_BOOTING > state before and it worked well and wasnt fragile. > > Our system_state semantics problems were more rooted in the fact > that the SYSTEM_BOOTING stage wasnt well defined. But if we did > a SYSTEM_SCHEDULER_BOOTING stage that would be pretty > bit-rot-safe. Actually, I should be able to simply use (system_state != SYSTEM_BOOTING), because the system state transitions to SYSTEM_RUNNING at essentially the same place that I set my new global variable. Especially given that this approach saves others from any bad guesses I might make about the existing uses of SYSTEM_BOOTING. ;-) I will also credit kmemcheck on the resulting patch. Thanx, Paul