Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752876AbaDXIhh (ORCPT ); Thu, 24 Apr 2014 04:37:37 -0400 Received: from e06smtp15.uk.ibm.com ([195.75.94.111]:58337 "EHLO e06smtp15.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752439AbaDXIhe (ORCPT ); Thu, 24 Apr 2014 04:37:34 -0400 Message-ID: <1398328643.2805.102.camel@ThinkPad-T5421.cn.ibm.com> Subject: Re: [RFC PATCH v5 1/2] Use lock_device_hotplug() in cpu_probe_store() and cpu_release_store() From: Li Zhong To: Tejun Heo Cc: LKML , gregkh@linuxfoundation.org, rafael.j.wysocki@intel.com, toshi.kani@hp.com Date: Thu, 24 Apr 2014 16:37:23 +0800 In-Reply-To: <20140423143940.GD4781@htj.dyndns.org> References: <20140415145017.GK1863@htj.dyndns.org> <1397612500.13188.83.camel@ThinkPad-T5421.cn.ibm.com> <20140416151749.GE1257@htj.dyndns.org> <1397717444.4034.15.camel@ThinkPad-T5421> <20140417151728.GK15326@htj.dyndns.org> <1398072059.2755.41.camel@ThinkPad-T5421.cn.ibm.com> <20140421223804.GD22730@htj.dyndns.org> <1398133777.2805.7.camel@ThinkPad-T5421.cn.ibm.com> <20140422204006.GA3615@mtj.dyndns.org> <1398218426.2805.42.camel@ThinkPad-T5421.cn.ibm.com> <20140423143940.GD4781@htj.dyndns.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14042408-0342-0000-0000-0000088A3867 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2014-04-23 at 10:39 -0400, Tejun Heo wrote: > On Wed, Apr 23, 2014 at 10:00:26AM +0800, Li Zhong wrote: > > If you remove cpu0, then the cpu0 directory will be removed, together > > with the "online" file in the directory, while some other process might > > be writing 0 or 1 to it. > > > > But here, for the probe/release, take "release" for example, if user > > writes something that stands for cpu0 to it, the cpu0 will be removed, > > and the cpu0 directory and the files under it will be removed. But > > "release" itself is not removed. > > > > They are attributes of cpu_subsys, not of some specific cpus. > > OIC, so the file itself which triggers removal doesn't get removed. > Hmmm... but can't you still fall into deadlock? If on/offline takes > the same lock under active protection which is also taken while > removing the cpu files, it doesn't really matter whether the release > file itself is removed in the process or not. You can still have ABBA > deadlock. What am I missing here? After thinking it harder, I still couldn't see ABBA here ... the active protection taken here is for "probe/release" which will not be waited for removing something like "online" under cpu#? Or my assumption that s_active for different files are different locks are completely wrong? Or I missed something else? Thanks, Zhong > > Thanks. > -- 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/