From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751095AbVK0QkN (ORCPT ); Sun, 27 Nov 2005 11:40:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751109AbVK0QkM (ORCPT ); Sun, 27 Nov 2005 11:40:12 -0500 Received: from fsmlabs.com ([168.103.115.128]:50080 "EHLO spamalot.fsmlabs.com") by vger.kernel.org with ESMTP id S1751095AbVK0QkL (ORCPT ); Sun, 27 Nov 2005 11:40:11 -0500 X-ASG-Debug-ID: 1133109604-366-74-0 X-Barracuda-URL: http://10.0.1.244:8000/cgi-bin/mark.cgi Date: Sun, 27 Nov 2005 08:45:47 -0800 (PST) From: Zwane Mwaikambo To: "Eric W. Biederman" cc: Andi Kleen , Linux Kernel , Andrew Morton , "Raj, Ashok" , Stephen Hemminger X-ASG-Orig-Subj: Re: [PATCH] i386/x86_64: Don't IPI to offline cpus on shutdown Subject: Re: [PATCH] i386/x86_64: Don't IPI to offline cpus on shutdown In-Reply-To: Message-ID: References: <20051127135833.GH20775@brahms.suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Barracuda-Spam-Score: 0.00 X-Barracuda-Spam-Status: No, SCORE=0.00 using global scores of TAG_LEVEL=1000.0 QUARANTINE_LEVEL=5.0 KILL_LEVEL=5.0 tests= X-Barracuda-Spam-Report: Code version 3.02, rules version 3.0.5625 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 27 Nov 2005, Eric W. Biederman wrote: > Andi Kleen writes: > > > On Sun, Nov 27, 2005 at 02:05:45AM -0800, Zwane Mwaikambo wrote: > >> http://bugzilla.kernel.org/show_bug.cgi?id=5203 > >> > >> There is a small race during SMP shutdown between the processor issuing > >> the shutdown and the other processors clearing themselves off the > >> cpu_online_map as they do this without using the normal cpu offline > >> synchronisation. To avoid this we should wait for all the other processors > >> to clear their corresponding bits and then proceed. This way we can safely > >> make the cpu_online test in smp_send_reschedule, it's safe during normal > >> runtime as smp_send_reschedule is called with a lock held / preemption > >> disabled. > > > > Looking at the backtrace in the bug - how can sys_reboot call do_exit??? > > I would say the problem is in whatever causes that. It shouldn't > > do that. sys_reboot shouldn't schedule, it's that simple. > > Your patch is just papering over that real bug. > > sys_reboot in the case of halt (after everything else is done) > has directly called do_exit for years. > > There are some very subtle interactions there. The one > I always remember (having found it the hard way) is that > interrupts must be left on so ctrl-alt-del still works. > > This do_exit may be something similar, although I can't > think of how it could be useful. I wondered the same thing, perhaps i am papering over the bug, what exactly is do_exit doing there?