From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753386AbaIXPDR (ORCPT ); Wed, 24 Sep 2014 11:03:17 -0400 Received: from terminus.zytor.com ([198.137.202.10]:60024 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754281AbaIXPDK (ORCPT ); Wed, 24 Sep 2014 11:03:10 -0400 Date: Wed, 24 Sep 2014 08:01:52 -0700 From: tip-bot for Wanpeng Li Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, peterz@infradead.org, linn@hp.com, stable@vger.kernel.org, toshi.kani@hp.com, wanpeng.li@linux.intel.com, srostedt@redhat.com, isimatu.yasuaki@jp.fujitsu.com, tglx@linutronix.de, prarit@redhat.com, rientjes@google.com, bp@suse.de Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, peterz@infradead.org, linn@hp.com, stable@vger.kernel.org, toshi.kani@hp.com, wanpeng.li@linux.intel.com, isimatu.yasuaki@jp.fujitsu.com, srostedt@redhat.com, tglx@linutronix.de, bp@suse.de, rientjes@google.com, prarit@redhat.com In-Reply-To: <1411547885-48165-1-git-send-email-wanpeng.li@linux.intel.com> References: <1411547885-48165-1-git-send-email-wanpeng.li@linux.intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] sched: Fix unreleased llc_shared_mask bit during CPU hotplug Git-Commit-ID: 03bd4e1f7265548832a76e7919a81f3137c44fd1 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 03bd4e1f7265548832a76e7919a81f3137c44fd1 Gitweb: http://git.kernel.org/tip/03bd4e1f7265548832a76e7919a81f3137c44fd1 Author: Wanpeng Li AuthorDate: Wed, 24 Sep 2014 16:38:05 +0800 Committer: Ingo Molnar CommitDate: Wed, 24 Sep 2014 15:13:20 +0200 sched: Fix unreleased llc_shared_mask bit during CPU hotplug The following bug can be triggered by hot adding and removing a large number of xen domain0's vcpus repeatedly: 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 Last level cache shared mask is built during CPU up and the build_sched_domain() routine takes advantage of it to setup the sched domain CPU topology. However, llc_shared_mask is not released during CPU disable, which leads to an invalid sched domainCPU topology. This patch fix it by releasing the llc_shared_mask correctly during CPU disable. Yasuaki also reported that this can happen on real hardware: https://lkml.org/lkml/2014/7/22/1018 His case is here: == Here is an 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 the wrong value. Signed-off-by: Wanpeng Li Tested-by: Linn Crosetto Reviewed-by: Borislav Petkov Reviewed-by: Toshi Kani Reviewed-by: Yasuaki Ishimatsu Cc: Cc: David Rientjes Cc: Prarit Bhargava Cc: Steven Rostedt Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1411547885-48165-1-git-send-email-wanpeng.li@linux.intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/smpboot.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 2d872e0..42a2dca 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1284,6 +1284,9 @@ static void remove_siblinginfo(int cpu) for_each_cpu(sibling, cpu_sibling_mask(cpu)) cpumask_clear_cpu(cpu, cpu_sibling_mask(sibling)); + for_each_cpu(sibling, cpu_llc_shared_mask(cpu)) + cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling)); + cpumask_clear(cpu_llc_shared_mask(cpu)); cpumask_clear(cpu_sibling_mask(cpu)); cpumask_clear(cpu_core_mask(cpu)); c->phys_proc_id = 0;