linux-kernel - Re: [PATCH v4] x86, hotplug: fix llc shared map unreleased during cpu hotplug

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Message-ID: <20140904085641.GA6311@kernel>
Date:	Thu, 4 Sep 2014 16:56:41 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	hpa@...or.com, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
	Borislav Petkov <bp@...en8.de>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Toshi Kani <toshi.kani@...com>, linux-kernel@...r.kernel.org,
	Zhang Yang <yang.z.zhang@...el.com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: Re: [PATCH v4] x86, hotplug: fix llc shared map unreleased during
 cpu hotplug

On Thu, Sep 04, 2014 at 07:20:34AM +0200, Ingo Molnar wrote:
>
>* Wanpeng Li <wanpeng.li@...ux.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
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