From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761437AbZFKIkb (ORCPT ); Thu, 11 Jun 2009 04:40:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759493AbZFKIkV (ORCPT ); Thu, 11 Jun 2009 04:40:21 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:64184 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1759231AbZFKIkU (ORCPT ); Thu, 11 Jun 2009 04:40:20 -0400 Message-ID: <4A30C346.8070406@cn.fujitsu.com> Date: Thu, 11 Jun 2009 16:41:42 +0800 From: Lai Jiangshan User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) MIME-Version: 1.0 To: Andrew Morton , paulmck@linux.vnet.ibm.com CC: ego@in.ibm.com, rusty@rustcorp.com.au, mingo@elte.hu, linux-kernel@vger.kernel.org, peterz@infradead.org, oleg@redhat.com, dipankar@in.ibm.com Subject: Re: [PATCH -mm resend] cpuhotplug: introduce try_get_online_cpus() take 3 References: <4A1F9CEA.1070705@cn.fujitsu.com> <20090530015342.GA21502@linux.vnet.ibm.com> <20090530043739.GA12157@in.ibm.com> <4A27708C.6030703@cn.fujitsu.com> <20090605153714.GB6778@linux.vnet.ibm.com> <20090608041934.GB17979@in.ibm.com> <20090608142520.GA6961@linux.vnet.ibm.com> <4A2E506D.9090107@cn.fujitsu.com> <20090609123438.b936137e.akpm@linux-foundation.org> <20090609234757.GH16117@linux.vnet.ibm.com> <4A2F08D6.6060309@cn.fujitsu.com> <20090609184238.06b38c3e.akpm@linux-foundation.org> In-Reply-To: <20090609184238.06b38c3e.akpm@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > > I still think we should really avoid having to do this. trylocks are > nasty things. > > Looking at the above, one would think that a correct fix would be to fix > the bug in "thread 2": take the locks in the correct order? As > try_get_online_cpus() doesn't actually have any callers, it's hard to > take that thought any further. > > Sometimes, we can not reorder the locks' order. try_get_online_cpus() is really needless when no one uses it. Paul's expedited RCU V7 may need it: http://lkml.org/lkml/2009/5/22/332 So this patch can be omitted when Paul does not use it. It's totally OK for me. Lai