From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755367AbZBWOCU (ORCPT ); Mon, 23 Feb 2009 09:02:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753840AbZBWOCC (ORCPT ); Mon, 23 Feb 2009 09:02:02 -0500 Received: from smtp116.mail.mud.yahoo.com ([209.191.84.165]:28146 "HELO smtp116.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753745AbZBWOCA (ORCPT ); Mon, 23 Feb 2009 09:02:00 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:X-YMail-OSG:X-Yahoo-Newman-Property:From:To:Subject:Date:User-Agent:Cc:References:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Content-Disposition:Message-Id; b=uVILUDDVAG2tyslswAKhG45f4rGIj+d7JtKEgvncY0AUm5ZSxgpmY96aeb0exqoJSxdbFdz/X4vDs+ozV6DXGVBBpo3//JI0STyY2bVQyQ8udenIUp0eH3sRHGPuLk/7K2CWAmv5pjIgZDQyxKwQ06ZTQsuMbTnMyidikqp30rw= ; X-YMail-OSG: dmzxchcVM1kx0PWQwZnqOWjpMKslIXzSnjUOM4OdDeSBWs7gZqoX5lg6khnLPbFdZKz_Snz4DguKzgafCkZnX2DHricF0HcW1tkMYEgGQOtk62dHK383_zpivJBszzgnG4UzAuS7lHIdKg93IaZf1VZ5SBnEfpnaipRVXB19aHF9.c8jHq_ozy3kXY7HXcDkwxgjqq0op71GD1pHvWlMukP5TVI- X-Yahoo-Newman-Property: ymail-3 From: Nick Piggin To: paulmck@linux.vnet.ibm.com Subject: Re: [PATCH] mm: fix lazy vmap purging (use-after-free error) Date: Tue, 24 Feb 2009 00:29:36 +1100 User-Agent: KMail/1.9.51 (KDE/4.0.4; ; ) Cc: Vegard Nossum , Ingo Molnar , stable@kernel.org, Andrew Morton , Nick Piggin , Pekka Enberg , linux-kernel@vger.kernel.org References: <20090220140157.GA12799@elte.hu> <20090222030030.GD6860@linux.vnet.ibm.com> <20090223051709.GA5990@linux.vnet.ibm.com> In-Reply-To: <20090223051709.GA5990@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200902240029.37815.nickpiggin@yahoo.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). 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/