From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754052Ab0C2QLc (ORCPT ); Mon, 29 Mar 2010 12:11:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57561 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753012Ab0C2QLb (ORCPT ); Mon, 29 Mar 2010 12:11:31 -0400 Message-ID: <4BB0D11A.607@redhat.com> Date: Mon, 29 Mar 2010 12:11:06 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.7) Gecko/20100120 Fedora/3.0.1-1.fc12 Lightning/1.0b2pre Thunderbird/3.0.1 MIME-Version: 1.0 To: Kent Overstreet CC: linux-kernel@vger.kernel.org, Peter Zijlstra Subject: Re: KVM bug, git bisected References: <4BADFD74.8060904@gmail.com> In-Reply-To: <4BADFD74.8060904@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/27/2010 08:43 AM, Kent Overstreet wrote: > commit 5beb49305251e5669852ed541e8e2f2f7696c53e > Author: Rik van Riel > Date: Fri Mar 5 13:42:07 2010 -0800 > > mm: change anon_vma linking to fix multi-process server scalability issue > > I get this when starting kvm. The warning hasn't caused me problems, but > I've also been getting a scheduling while atomic panic when I start kvm > that I can only reproduce when I don't want to. It's definitely config > dependent, I'd guess preempt might have something to do with it. From your trace, it looks like mm_take_all_locks is taking close to 256 locks, which is where the preempt_count could overflow into the softirq count. Since kvm-qemu is exec'd, I am guessing you have a very large number of VMAs in your qemu process. Is that correct? Peter, would it be safe to increase PREEMPT_BITS to eg. 10? > [ 44.418510] ------------[ cut here ]------------ > [ 44.418554] WARNING: at kernel/sched.c:3554 add_preempt_count+0x9c/0xa0() > [ 44.418591] Hardware name: P5K-E > [ 44.418623] Modules linked in: > [ 44.418686] Pid: 1486, comm: kvm Not tainted 2.6.33 #31 > [ 44.418721] Call Trace: > [ 44.418765] [] warn_slowpath_common+0x7b/0xc0 > [ 44.418810] [] warn_slowpath_null+0x14/0x20 > [ 44.418854] [] add_preempt_count+0x9c/0xa0 > [ 44.418898] [] _raw_spin_lock+0x1b/0x40 > [ 44.418943] [] mm_take_all_locks+0x11a/0x160 > [ 44.418988] [] do_mmu_notifier_register+0x7b/0x1d0 > [ 44.419032] [] mmu_notifier_register+0x13/0x20 > [ 44.419078] [] kvm_dev_ioctl+0x238/0x490 > [ 44.419122] [] ? sub_preempt_count+0x9/0xa0 > [ 44.419167] [] vfs_ioctl+0x3d/0xd0 > [ 44.419209] [] do_vfs_ioctl+0x88/0x570 > [ 44.419252] [] ? add_preempt_count+0x9/0xa0 > [ 44.419294] [] sys_ioctl+0x81/0xa0 > [ 44.419336] [] system_call_fastpath+0x16/0x1b > [ 44.419378] ---[ end trace 34e3b440ad5088d0 ]---