From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756870AbYKUS6z (ORCPT ); Fri, 21 Nov 2008 13:58:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752040AbYKUS6s (ORCPT ); Fri, 21 Nov 2008 13:58:48 -0500 Received: from smtp-out.google.com ([216.239.45.13]:22433 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751838AbYKUS6r (ORCPT ); Fri, 21 Nov 2008 13:58:47 -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=phqZLC5caoZnEO6rmr/QNU8NlhbRdBiDtSSSt+EHQi1fP/5yeTJ9PpYo3YtS7cQZq dmcB3ZCh7Z0wH5yoaFm0g== MIME-Version: 1.0 In-Reply-To: <4926762A.7000602@cn.fujitsu.com> References: <4926762A.7000602@cn.fujitsu.com> Date: Fri, 21 Nov 2008 10:58:44 -0800 Message-ID: <6599ad830811211058q3fe12e5coa62436e777b60f1a@mail.gmail.com> Subject: Re: [PATCH 1/2] cgroups: enhance task_cgroup() 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_cgroup() calls cgroup_subsys_state(). No, it calls task_subsys_state() > and we must use rcu_read_lock() to protect cgroup_subsys_state(). > so we must use rcu_read_lock() to protect task_cgroup(). > > but it'll not so friendly to caller: the callers of task_cgroup() have > held cgroup_lock(). it means that struct cgroup will not be freed. > > So this patch add rcu_read_lock() in task_cgroup() to enhance task_cgroup(). > And we do NOT NEED FIX task_cgroup()'s callers, and cgroup_lock() > can protect task_cgroup(). Is there a reason to add an implicit rcu_read_lock() in task_cgroup() and not directly in task_subsys_state() ? Paul > > Signed-off-by: Lai Jiangshan > --- > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > index 1164963..22901ff 100644 > --- a/include/linux/cgroup.h > +++ b/include/linux/cgroup.h > @@ -359,6 +360,10 @@ > static inline struct cgroup* task_cgroup(struct task_struct *task, > int subsys_id) > { > - return task_subsys_state(task, subsys_id)->cgroup; > + struct cgroup *ret; > + rcu_read_lock(); > + ret = task_subsys_state(task, subsys_id)->cgroup; > + rcu_read_unlock(); > + return ret; > } > > int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *ss, > > >