From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1759352Ab0BYPgS (ORCPT <rfc822;w@1wt.eu>);
	Thu, 25 Feb 2010 10:36:18 -0500
Received: from mail-px0-f204.google.com ([209.85.216.204]:43256 "EHLO
	mail-px0-f204.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1759190Ab0BYPgQ convert rfc822-to-8bit (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 25 Feb 2010 10:36:16 -0500
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:in-reply-to:references:date:message-id:subject:from:to
         :cc:content-type:content-transfer-encoding;
        b=vLidE8Xtagb9pt1xbsg9VnltQTxLiYgBRctC7ECy5EFIaoqB9Lc6ZrOXDOsOIa6Y75
         M1EtbZ3drqACIu2CWtpK1+mKnxEpPaCWRUoMqCj/yFArQ/vTGrasYUqdWY4nVEcjvy0b
         wbbKuiPwZ8GTqk4PfPBMvqPe5Il17vr4eBZPw=
MIME-Version: 1.0
In-Reply-To: <20100223115846.GI1882@linux>
References: <1266765525-30890-1-git-send-email-arighi@develer.com>
	 <1266765525-30890-2-git-send-email-arighi@develer.com>
	 <alpine.DEB.2.00.1002211321010.22858@chino.kir.corp.google.com>
	 <20100221221700.GA5233@linux> <20100222180732.GC3096@redhat.com>
	 <20100223115846.GI1882@linux>
Date: Fri, 26 Feb 2010 00:36:15 +0900
Message-ID: <28c262361002250736k57543379j8291e0dfb8df194e@mail.gmail.com>
Subject: Re: [PATCH 1/2] memcg: dirty pages accounting and limiting 
	infrastructure
From: Minchan Kim <minchan.kim@gmail.com>
To: Andrea Righi <arighi@develer.com>
Cc: Vivek Goyal <vgoyal@redhat.com>, David Rientjes <rientjes@google.com>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Suleiman Souhlal <suleiman@google.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi

On Tue, Feb 23, 2010 at 8:58 PM, Andrea Righi <arighi@develer.com> wrote:
> On Mon, Feb 22, 2010 at 01:07:32PM -0500, Vivek Goyal wrote:
>> > > > +unsigned long mem_cgroup_dirty_bytes(void)
>> > > > +{
>> > > > +       struct mem_cgroup *memcg;
>> > > > +       unsigned long dirty_bytes;
>> > > > +
>> > > > +       if (mem_cgroup_disabled())
>> > > > +               return vm_dirty_bytes;
>> > > > +
>> > > > +       rcu_read_lock();
>> > > > +       memcg = mem_cgroup_from_task(current);
>> > > > +       if (memcg == NULL)
>> > > > +               dirty_bytes = vm_dirty_bytes;
>> > > > +       else
>> > > > +               dirty_bytes = get_dirty_bytes(memcg);
>> > > > +       rcu_read_unlock();
>> > >
>> > > The rcu_read_lock() isn't protecting anything here.
>> >
>> > Right!
>>
>> Are we not protecting "memcg" pointer using rcu here?
>
> Vivek, you are right:
>
>  mem_cgroup_from_task() -> task_subsys_state() -> rcu_dereference()
>
> So, this *must* be RCU protected.

So, Doesn't mem_cgroup_from_task in mem_cgroup_can_attach need RCU, too?


-- 
Kind regards,
Minchan Kim