From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757300AbZBWQti (ORCPT ); Mon, 23 Feb 2009 11:49:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753289AbZBWQta (ORCPT ); Mon, 23 Feb 2009 11:49:30 -0500 Received: from e5.ny.us.ibm.com ([32.97.182.145]:37492 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752783AbZBWQt3 (ORCPT ); Mon, 23 Feb 2009 11:49:29 -0500 Date: Mon, 23 Feb 2009 08:17:26 -0800 From: "Paul E. McKenney" To: Nick Piggin Cc: Vegard Nossum , Ingo Molnar , 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: <20090223161726.GD6751@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090220140157.GA12799@elte.hu> <20090222030030.GD6860@linux.vnet.ibm.com> <20090223051709.GA5990@linux.vnet.ibm.com> <200902240029.37815.nickpiggin@yahoo.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200902240029.37815.nickpiggin@yahoo.com.au> 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 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. Thanx, Paul > Vegard, I would like to still use your patch in vmalloc.c as well. It > solves a possible use-after-free with preemptible RCU, and also helps with > a patch I have to conditionally disable lazy vmap unmapping (for Xen). > > We _could_ disable RCU there instead to solve the preemptible RCU bug, but > your patch I think is less overhead. > > So with appropriate changelog update, please also resend your patch > (with Acked-by: Nick Piggin ) > > Thanks, > Nick > > > Located-by: Vegard Nossum > > Signed-off-by: Paul E. McKenney > > --- > > > > 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(); > > diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c > > index bd5a900..a758fa6 100644 > > --- a/kernel/rcuclassic.c > > +++ b/kernel/rcuclassic.c > > @@ -678,8 +678,10 @@ int rcu_needs_cpu(int cpu) > > */ > > void rcu_check_callbacks(int cpu, int user) > > { > > + extern int idle_task_is_really_idle; > > + > > if (user || > > - (idle_cpu(cpu) && !in_softirq() && > > + (idle_cpu(cpu) && idle_task_is_really_idle && !in_softirq() && > > hardirq_count() <= (1 << HARDIRQ_SHIFT))) { > > > > /* > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index b2fd602..e996d85 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -947,8 +947,10 @@ static void rcu_do_batch(struct rcu_data *rdp) > > */ > > void rcu_check_callbacks(int cpu, int user) > > { > > + extern int idle_task_is_really_idle; > > + > > if (user || > > - (idle_cpu(cpu) && !in_softirq() && > > + (idle_cpu(cpu) && idle_task_is_really_idle && !in_softirq() && > > hardirq_count() <= (1 << HARDIRQ_SHIFT))) { > > > > /* > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at http://www.tux.org/lkml/ > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/