From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1756737AbaIDIzB (ORCPT <rfc822;w@1wt.eu>);
	Thu, 4 Sep 2014 04:55:01 -0400
Received: from mga11.intel.com ([192.55.52.93]:16326 "EHLO mga11.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1756208AbaIDIy5 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Thu, 4 Sep 2014 04:54:57 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="4.97,862,1389772800"; 
   d="scan'208";a="381275096"
Date: Thu, 4 Sep 2014 16:56:41 +0800
From: Wanpeng Li <wanpeng.li@linux.intel.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: hpa@zytor.com, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        Borislav Petkov <bp@alien8.de>,
        Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
        David Rientjes <rientjes@google.com>,
        Prarit Bhargava <prarit@redhat.com>,
        Steven Rostedt <srostedt@redhat.com>,
        Jan Kiszka <jan.kiszka@siemens.com>, Toshi Kani <toshi.kani@hp.com>,
        linux-kernel@vger.kernel.org, Zhang Yang <yang.z.zhang@intel.com>,
        Wanpeng Li <wanpeng.li@linux.intel.com>
Subject: Re: [PATCH v4] x86, hotplug: fix llc shared map unreleased during
 cpu hotplug
Message-ID: <20140904085641.GA6311@kernel>
Reply-To: Wanpeng Li <wanpeng.li@linux.intel.com>
References: <1406625883-4972-1-git-send-email-wanpeng.li@linux.intel.com>
 <20140904052034.GA29146@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20140904052034.GA29146@gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Sep 04, 2014 at 07:20:34AM +0200, Ingo Molnar wrote:
>
>* Wanpeng Li <wanpeng.li@linux.intel.com> 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
>> 
>> 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.
>
>Very little is said in this changelog about how the bug was 
>found, how likely it is to occur for others, what systems are 
>affected, etc.

This bug can be triggered by hot add and remove large number of xen 
domain0's vcpus repeated.

Regards,
Wanpeng Li 

>
>Thanks,
>
>	Ingo