From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751161AbWGWI3s (ORCPT ); Sun, 23 Jul 2006 04:29:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751158AbWGWI3s (ORCPT ); Sun, 23 Jul 2006 04:29:48 -0400 Received: from [216.208.38.107] ([216.208.38.107]:13708 "EHLO OTTLS.pngxnet.com") by vger.kernel.org with ESMTP id S1751157AbWGWI3r (ORCPT ); Sun, 23 Jul 2006 04:29:47 -0400 Subject: Re: remove cpu hotplug bustification in cpufreq. From: Arjan van de Ven To: Andrew Morton Cc: Ingo Molnar , ashok.raj@intel.com, linux-kernel@vger.kernel.org, davej@redhat.com, Linus Torvalds In-Reply-To: <20060722223425.c94a858e.akpm@osdl.org> References: <20060722194018.GA28924@redhat.com> <20060722180602.ac0d36f5.akpm@osdl.org> <20060722223425.c94a858e.akpm@osdl.org> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Sun, 23 Jul 2006 10:29:40 +0200 Message-Id: <1153643380.7359.24.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, > > Well, I just got Ashok's trial patches which turns the thing into a rwsem > > as I outlined earlier. > > Mark my words ;) > > > I'll try them out. If they don't work, we should just delete the lock and > > go totally back to square 1. > > rwsem conversion has the potential to merely hide the problem. Ingo, does > lockdep detect recursive down_read()? lockdep detects and warns about those. I think we're about equally skeptical about this; I'm extremely hesitant about any place in the kernel that uses rwsems for anything other than a performance tweak. I've ended up with a mental model of rwsems that basically comes down to "you need to be able to replace it with a mutex without breaking correctness". Now of course that model is somewhat of an oversimplification, but not by that much... Greetings, Arjan van de Ven