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

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Message-ID: <20140904093414.GA7296@kernel>
Date:	Thu, 4 Sep 2014 17:34:14 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Ingo Molnar <mingo@...hat.com>
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

Hi Ingo,
On Thu, Sep 04, 2014 at 04:56:41PM +0800, Wanpeng Li wrote:
>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.
>

If I need to send a new version of the patch or you can pick the patch
w/ the updated changelog for me? ;-)

Regards,
Wanpeng Li 

>Regards,
>Wanpeng Li 
>
>>
>>Thanks,
>>
>>	Ingo
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