From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754464AbaIWEsg (ORCPT ); Tue, 23 Sep 2014 00:48:36 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:34934 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751878AbaIWEsb (ORCPT ); Tue, 23 Sep 2014 00:48:31 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v2.2.3 X-SHieldMailCheckerPolicyVersion: FJ-ISEC-20140219-2 Message-ID: <5420FB25.8050102@jp.fujitsu.com> Date: Tue, 23 Sep 2014 13:46:29 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Wanpeng Li , Ingo Molnar , , Peter Zijlstra CC: Ingo Molnar , , Borislav Petkov , Yasuaki Ishimatsu , David Rientjes , Prarit Bhargava , Steven Rostedt , Toshi Kani , Subject: Re: [PATCH v5] x86, cpu-hotplug: fix llc shared map unreleased during cpu hotplug References: <1410938272-7217-1-git-send-email-wanpeng.li@linux.intel.com> In-Reply-To: <1410938272-7217-1-git-send-email-wanpeng.li@linux.intel.com> Content-Type: text/plain; charset="ISO-2022-JP" Content-Transfer-Encoding: 7bit X-SecurityPolicyCheck-GC: OK by FENCE-Mail X-TM-AS-MML: No Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2014/09/17 16:17), Wanpeng Li wrote: > BUG: unable to handle kernel NULL pointer dereference at 0000000000000004 > IP: [..] find_busiest_group > PGD 5a9d5067 PUD 13067 PMD 0 > Oops: 0000 [#3] SMP > [...] > Call Trace: > load_balance > ? _raw_spin_unlock_irqrestore > idle_balance > __schedule > schedule > schedule_timeout > ? lock_timer_base > schedule_timeout_uninterruptible > msleep > lock_device_hotplug_sysfs > online_store > dev_attr_store > sysfs_write_file > vfs_write > SyS_write > system_call_fastpath > > This bug can be triggered by hot add and remove large number of xen > domain0's vcpus repeatedly. > > Last level cache shared map is built during cpu up and build sched domain > routine takes advantage of it to setup sched domain cpu topology, however, > llc shared map is unreleased during cpu disable which lead to invalid sched > domain cpu topology. This patch fix it by release llc shared map correctly > during cpu disable. > > Reviewed-by: Toshi Kani > Reviewed-by: Yasuaki Ishimatsu > Tested-by: Linn Crosetto > Signed-off-by: Wanpeng Li Yasuaki reported this can happen on our real hardware. https://lkml.org/lkml/2014/7/22/1018 Our case is here. == Here is a example on my system. My system has 4 sockets and each socket has 15 cores and HT is enabled. In this case, each core of sockes is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 Socket#2 | 30-44, 90-104 Socket#3 | 45-59, 105-119 Then llc_shared_mask of CPU#30 has 0x3fff80000001fffc0000000. It means that last level cache of Socket#2 is shared with CPU#30-44 and 90-104. When hot-removing socket#2 and #3, each core of sockets is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 But llc_shared_mask is not cleared. So llc_shared_mask of CPU#30 remains having 0x3fff80000001fffc0000000. After that, when hot-adding socket#2 and #3, each core of sockets is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 Socket#2 | 30-59 Socket#3 | 90-119 Then llc_shared_mask of CPU#30 becomes 0x3fff8000fffffffc0000000. It means that last level cache of Socket#2 is shared with CPU#30-59 and 90-104. So the mask has wrong value. At first, I cleared hot-removed CPU number's bit from llc_shared_map when hot removing CPU. But Borislav suggested that the problem will disappear if readded CPU is assigned same CPU number. And llc_shared_map must not be changed. == So, please. Thanks, -Kame