From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759221AbYH2VU4 (ORCPT ); Fri, 29 Aug 2008 17:20:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755443AbYH2VUs (ORCPT ); Fri, 29 Aug 2008 17:20:48 -0400 Received: from one.firstfloor.org ([213.235.205.2]:48982 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756123AbYH2VUs (ORCPT ); Fri, 29 Aug 2008 17:20:48 -0400 Date: Fri, 29 Aug 2008 23:23:30 +0200 From: Andi Kleen To: "Paul E. McKenney" Cc: Andi Kleen , rusty@rustcorp.com.au, linux-kernel@vger.kernel.org, akpm@osdl.org Subject: Re: [PATCH] Remove stop_machine during module load Message-ID: <20080829212330.GC26610@one.firstfloor.org> References: <20080829191734.GA28329@basil.nowhere.org> <20080829204457.GF6725@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080829204457.GF6725@linux.vnet.ibm.com> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, Thanks for the excellent review. On Fri, Aug 29, 2008 at 01:44:57PM -0700, Paul E. McKenney wrote: > > OK, what about the read side? Not so good for __unlink_module() to yank That's independent from my patch isn't it? I don't think I'm changing anything here. All of the issues you're pointing out are already in the code (except for the missing read_barrier_depends() perhaps) I think the lockless users like oops or sysrq-t typically have preemption disabled, so they should be ok regarding that. > the module out from under a reader. Therefore, all readers must either > disable interrupts to block stop_machine() or must hold some sort of > mutex that prevents modules from being unloaded. > > First, where the heck -is- the read side... > > o each_symbol() needs its list_for_each_entry() to become > list_for_each_entry_rcu() and needs local_irq_disable() Ah that's needed for the Alpha barrier depends semantics, right? > Yet another approach would be to use call_rcu() to defer the > various kfree() &c calls later in free_module. I think that would be a the better approach. -Andi