From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756691AbYKUSgs (ORCPT ); Fri, 21 Nov 2008 13:36:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751445AbYKUSgk (ORCPT ); Fri, 21 Nov 2008 13:36:40 -0500 Received: from smtp-out.google.com ([216.239.45.13]:17926 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751178AbYKUSgj (ORCPT ); Fri, 21 Nov 2008 13:36:39 -0500 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:date:message-id:subject:from:to: cc:content-type:content-transfer-encoding; b=aKNxDgpoQEyrk1nsf4VqXC5S61nChQgvBGRpdJxaR5BEhcdMXyYY+mNi6ZmETON5b UTpsIMURdilx202/CQJxQ== MIME-Version: 1.0 In-Reply-To: <49267621.2070706@cn.fujitsu.com> References: <49267621.2070706@cn.fujitsu.com> Date: Fri, 21 Nov 2008 10:36:37 -0800 Message-ID: <6599ad830811211036k419ff716h6068d532c9942d73@mail.gmail.com> Subject: Re: [PATCH] cpuset: rcu_read_lock() to protect task_cs() From: Paul Menage To: Lai Jiangshan Cc: Andrew Morton , Linux Kernel Mailing List , Linux Containers Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 21, 2008 at 12:49 AM, Lai Jiangshan wrote: > > task_cs() calls cgroup_subsys_state(). You mean it calls task_subsys_state(). > > we must use rcu_read_lock() to protect cgroup_subsys_state(). > > it's correct that top_cpuset is never freed, but cgroup_subsys_state() > accesses css_set, this css_set maybe freed when task_cs() called. It would be nice to have an RCU debug mode where rcu_dereference() does a WARN() if it's invoked not under rcu_read_lock(). > > we use use rcu_read_lock() to protect it. > > Signed-off-by: Lai Jiangshan > --- > diff --git a/kernel/cpuset.c b/kernel/cpuset.c > index 3e00526..e0e087e 100644 > --- a/kernel/cpuset.c > +++ b/kernel/cpuset.c > @@ -363,14 +363,9 @@ void cpuset_update_task_memory_state(void) > struct task_struct *tsk = current; > struct cpuset *cs; > > - if (task_cs(tsk) == &top_cpuset) { > - /* Don't need rcu for top_cpuset. It's never freed. */ > - my_cpusets_mem_gen = top_cpuset.mems_generation; > - } else { > - rcu_read_lock(); > - my_cpusets_mem_gen = task_cs(tsk)->mems_generation; > - rcu_read_unlock(); > - } > + rcu_read_lock(); > + my_cpusets_mem_gen = task_cs(tsk)->mems_generation; > + rcu_read_unlock(); Yes, I guess this old cpusets assumption is no longer valid in cgroups. Acked-by: Paul Menage Thanks Paul