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

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Date:	Tue, 16 Sep 2014 11:01:12 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, hpa@...or.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>
Subject: Re: [PATCH v4] x86, hotplug: fix llc shared map unreleased during
 cpu hotplug


* Wanpeng Li <wanpeng.li@...ux.intel.com> wrote:

> 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? ;-)

Please send a fresh new version, maintainers trying to splice & 
dice patches and changelogs is an unrobust approach prone to 
mistakes.

Thanks,

	Ingo
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