From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754976AbaDNUNY (ORCPT ); Mon, 14 Apr 2014 16:13:24 -0400 Received: from mail-qg0-f43.google.com ([209.85.192.43]:46441 "EHLO mail-qg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754817AbaDNUNT (ORCPT ); Mon, 14 Apr 2014 16:13:19 -0400 Date: Mon, 14 Apr 2014 16:13:15 -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: <20140414201315.GD16835@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1397461649.12943.1.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 Mon, Apr 14, 2014 at 03:47:29PM +0800, Li Zhong wrote: > @@ -439,6 +439,7 @@ static ssize_t online_store(struct device *dev, struct device_attribute *attr, > { > bool val; > int ret; > + struct kernfs_node *kn; > > ret = strtobool(buf, &val); > if (ret < 0) > @@ -448,7 +449,19 @@ static ssize_t online_store(struct device *dev, struct device_attribute *attr, > if (ret) > return ret; > > + kn = kernfs_find_and_get(dev->kobj.sd, attr->attr.name); > + if (WARN_ON_ONCE(!kn)) > + goto out; > + > + get_device(dev); > + kernfs_break_active_protection(kn); > ret = val ? device_online(dev) : device_offline(dev); > + kernfs_unbreak_active_protection(kn); > + put_device(dev); > + > + kernfs_put(kn); > + > +out: > unlock_device_hotplug(); > return ret < 0 ? ret : count; > } Can you please add comment explainin why this is being down? As it currently stands, it's quite a bit of complexity without any indication what's going on why. Also, if device_hotplug is locked, is it really necessary to get @dev? Can it go away inbetween? The code snippet looks weird because getting @dev indicates that the device might go away without doing it but then it proceeds to invoke device_{on|off}line() which probably isn't safe to invoke on a removed device. Thanks. -- tejun