From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422665AbaDPPRy (ORCPT ); Wed, 16 Apr 2014 11:17:54 -0400 Received: from mail-qg0-f49.google.com ([209.85.192.49]:57564 "EHLO mail-qg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161469AbaDPPRx (ORCPT ); Wed, 16 Apr 2014 11:17:53 -0400 Date: Wed, 16 Apr 2014 11:17:49 -0400 From: Tejun Heo To: Li Zhong Cc: LKML , gregkh@linuxfoundation.org, rafael.j.wysocki@intel.com, toshi.kani@hp.com Subject: Re: [RFC PATCH v3] Use kernfs_break_active_protection() for device online store callbacks Message-ID: <20140416151749.GE1257@htj.dyndns.org> References: <1397121514.25199.91.camel@ThinkPad-T5421.cn.ibm.com> <20140410133116.GB25308@htj.dyndns.org> <1397189445.3649.14.camel@ThinkPad-T5421> <20140411102649.GB26252@mtj.dyndns.org> <1397461649.12943.1.camel@ThinkPad-T5421.cn.ibm.com> <20140414201315.GD16835@htj.dyndns.org> <1397529877.13188.68.camel@ThinkPad-T5421.cn.ibm.com> <20140415145017.GK1863@htj.dyndns.org> <1397612500.13188.83.camel@ThinkPad-T5421.cn.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1397612500.13188.83.camel@ThinkPad-T5421.cn.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Wed, Apr 16, 2014 at 09:41:40AM +0800, Li Zhong wrote: > > If so, that is > > an actually possible deadlock, no? > > Yes, but it seems to me that it is solved in commit 5e33bc41, which uses > lock_device_hotplug_sysfs() to return a restart syscall error if not > able to try lock the device_hotplug_lock. That also requires the device > removing code path to take the device_hotplug_lock. But that patch only takes out device_hotplug_lock out of the dependency graph and does nothing for cpu_add_remove_lock. It seems to be that there still is a deadlock condition involving s_active and cpu_add_remove_lock. Am I missing something here? Now that kernfs has a proper mechanism to deal with it, wouldn't it make more sense to replace 5e33bc41 with prper s_active protection breaking? Thanks. -- tejun