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

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Message-ID: <20140904090225.GA6555@kernel>
Date:	Thu, 4 Sep 2014 17:02:25 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>, hpa@...or.com,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
	Borislav Petkov <bp@...en8.de>,
	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>
Subject: Re: [PATCH v4] x86, hotplug: fix llc shared map unreleased during
 cpu hotplug

On Thu, Sep 04, 2014 at 02:40:07PM +0900, Yasuaki Ishimatsu wrote:
>(2014/09/04 14:20), 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.
>
>Hi Wanpeng,

Hi Yasuaki,

>
>In my understanding, the panic occurs by just onlining CPU as follows:
>echo 1 > /sys/devices/system/cpu/cpuX/online
>

See my reply to Ingo.

Regards,
Wanpeng Li 

>So, how about add the information?
>
>Thanks,
>Yasuaki Ishimatsu
>
>
>>
>>Thanks,
>>
>>	Ingo
>>
>
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