From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757725Ab2IXSta (ORCPT ); Mon, 24 Sep 2012 14:49:30 -0400 Received: from e28smtp06.in.ibm.com ([122.248.162.6]:42654 "EHLO e28smtp06.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757648Ab2IXSt1 (ORCPT ); Mon, 24 Sep 2012 14:49:27 -0400 Message-ID: <5060AB0E.3070809@linux.vnet.ibm.com> Date: Tue, 25 Sep 2012 00:18:46 +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: Borislav Petkov CC: Conny Seidel , Jan Kara , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Fengguang Wu , Peter Zijlstra , Andrew Morton , Johannes Weiner , "Paul E. McKenney" Subject: Re: divide error: bdi_dirty_limit+0x5a/0x9e References: <20120924102324.GA22303@aftab.osrc.amd.com> <20120924142305.GD12264@quack.suse.cz> <20120924143609.GH22303@aftab.osrc.amd.com> <20120924201650.6574af64.conny.seidel@amd.com> <20120924181927.GA25762@aftab.osrc.amd.com> In-Reply-To: <20120924181927.GA25762@aftab.osrc.amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit x-cbid: 12092418-9574-0000-0000-0000049117C4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/24/2012 11:49 PM, Borislav Petkov wrote: > On Mon, Sep 24, 2012 at 08:16:50PM +0200, Conny Seidel wrote: >> Hi, >> >> On Mon, 24 Sep 2012 16:36:09 +0200 >> Borislav Petkov wrote: >>> [ … ] >>> >>> Conny, would you test pls? >> >> Sure thing. >> Out of ~25 runs I only triggered it once, without the patch the >> trigger-rate is higher. >> >> [ 55.098249] Broke affinity for irq 81 >> [ 55.105108] smpboot: CPU 1 is now offline >> [ 55.311216] smpboot: Booting Node 0 Processor 1 APIC 0x11 >> [ 55.333022] LVT offset 0 assigned for vector 0x400 >> [ 55.545877] smpboot: CPU 2 is now offline >> [ 55.753050] smpboot: Booting Node 0 Processor 2 APIC 0x12 >> [ 55.775582] LVT offset 0 assigned for vector 0x400 >> [ 55.986747] smpboot: CPU 3 is now offline >> [ 56.193839] smpboot: Booting Node 0 Processor 3 APIC 0x13 >> [ 56.212643] LVT offset 0 assigned for vector 0x400 >> [ 56.423201] Got negative events: -25 > > I see it: > > __percpu_counter_sum does for_each_online_cpu without doing > get/put_online_cpus(). > Maybe I'm missing something, but that doesn't immediately tell me what's the exact source of the bug.. Note that there is a hotplug callback percpu_counter_hotcpu_callback() that takes the same fbc->lock before updating/resetting the percpu counters of offline CPU. So, though the synchronization is a bit weird, I don't immediately see a problematic race condition there. And, speaking of hotplug callbacks, on a slightly different note, I see one defined as ratelimit_handler(), which calls writeback_set_ratelimit() for *every single* state change in the hotplug sequence! Is that really intentional? num_online_cpus() changes its value only -once- for every hotplug :-) Regards, Srivatsa S. Bhat