From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752201AbaETKoH (ORCPT ); Tue, 20 May 2014 06:44:07 -0400 Received: from e23smtp03.au.ibm.com ([202.81.31.145]:45638 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751092AbaETKoF (ORCPT ); Tue, 20 May 2014 06:44:05 -0400 Message-ID: <537B319D.30603@linux.vnet.ibm.com> Date: Tue, 20 May 2014 16:12:37 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120828 Thunderbird/15.0 MIME-Version: 1.0 To: Peter Zijlstra CC: Oleg Nesterov , Tejun Heo , akpm@linux-foundation.org, fweisbec@gmail.com, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, mingo@kernel.org, rusty@rustcorp.com.au, hch@infradead.org, mgorman@suse.de, riel@redhat.com, bp@suse.de, rostedt@goodmis.org, mgalbraith@suse.de, ego@linux.vnet.ibm.com, rjw@rjwysocki.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 UPDATEDv3 3/3] CPU hotplug, smp: Flush any pending IPI callbacks before CPU offline References: <20140515191938.GB21306@htj.dyndns.org> <537514D3.4060308@linux.vnet.ibm.com> <20140515193656.GM4570@linux.vnet.ibm.com> <537518D6.6030006@linux.vnet.ibm.com> <5379F6BD.1090809@linux.vnet.ibm.com> <20140519161836.GA30387@redhat.com> <537A6060.7070406@linux.vnet.ibm.com> <537A6811.50808@linux.vnet.ibm.com> <20140520094203.GU2485@laptop.programming.kicks-ass.net> <537B29F7.6060104@linux.vnet.ibm.com> <20140520102542.GW2485@laptop.programming.kicks-ass.net> <537B2F09.5020306@linux.vnet.ibm.com> <537B309C.7000100@linux.vnet.ibm.com> In-Reply-To: <537B309C.7000100@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14052010-6102-0000-0000-0000059DD7C1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/20/2014 04:08 PM, Srivatsa S. Bhat wrote: > On 05/20/2014 04:01 PM, Srivatsa S. Bhat wrote: >> On 05/20/2014 03:55 PM, Peter Zijlstra wrote: >>> On Tue, May 20, 2014 at 03:39:59PM +0530, Srivatsa S. Bhat wrote: >>>>> The multi_cpu_stop() path isn't exclusive to hotplug, so your changelog >>>>> is wrong or the patch is. >>>>> >>>> >>>> Yes, I know that multi_cpu_stop() isn't exclusive to hotplug. That's why >>>> I have explicitly referred to CPU hotplug in the comment as well as the >>>> changelog. >>>> >>>> But I totally agree that code-wise this is not the best way to do it since >>>> this affects (although harmlessly) usecases other than hotplug as well. >>>> >>>> Do you have any other suggestions? >>> >>> How about making a kernel/smp.c hotplug notifier and stuffing it in the >>> CPU_DYING list? That's typically after we've already torn down the >>> interrupts for that cpu, so no chance of any new ones coming in. >>> >>> Or is that too late? >>> >> >> No, that should work just fine. Thank you for the suggestion! I'll give >> it a shot. >> > > The only problem will be that CPU_DYING notifiers are run after marking > the CPU offline, and hence the warning will trigger. We can avoid that by > defining a __generic_smp_call_function_single_interrupt() that doesn't > check for cpu_online(smp_processor_id) and call this function from the > hotplug notifier. > > (And that's probably something to fix while cleaning up hotplug later: Why should we mark the CPU offline _before_ running CPU_DYING? It makes more sense to mark it offline _after_ running CPU_DYING notifiers. I'll audit that path as well and see what I can find). Regards, Srivatsa S. Bhat