Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756660AbaDWOXy (ORCPT ); Wed, 23 Apr 2014 10:23:54 -0400 Received: from mail-qa0-f46.google.com ([209.85.216.46]:47537 "EHLO mail-qa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754814AbaDWOXu (ORCPT ); Wed, 23 Apr 2014 10:23:50 -0400 Date: Wed, 23 Apr 2014 10:23:46 -0400 From: Tejun Heo To: "Rafael J. Wysocki" Cc: Li Zhong , LKML , gregkh@linuxfoundation.org, toshi.kani@hp.com Subject: Re: [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks Message-ID: <20140423142346.GB4781@htj.dyndns.org> References: <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> <1398072230.2755.43.camel@ThinkPad-T5421.cn.ibm.com> <20140421224606.GE22730@htj.dyndns.org> <1398137679.2805.28.camel@ThinkPad-T5421.cn.ibm.com> <20140422204455.GB3615@mtj.dyndns.org> <5356EB6D.3010102@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5356EB6D.3010102@intel.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, Rafael. On Wed, Apr 23, 2014 at 12:21:33AM +0200, Rafael J. Wysocki wrote: > Can you please elaborate a bit? Because it can get involved in larger locking dependency issues by joining dependency graphs of two otherwise largely disjoint subsystems. It has potential to create possible deadlocks which don't need to exist. > It is there to protect hotplug operations involving multiple devices > (in different subsystems) from racing with each other. Why exactly > is it bad? But why would different subsystems, say cpu and memory, use the same lock? Wouldn't those subsystems already have proper locking inside their own subsystems? Why add this additional global lock across multiple subsystems? Thanks. -- tejun -- 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/