linux-kernel - Re: [PATCH v5] x86, cpu-hotplug: fix llc shared map unreleased during cpu hotplug

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Date:	Tue, 23 Sep 2014 11:37:53 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Toshi Kani <toshi.kani@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] x86, cpu-hotplug: fix llc shared map unreleased
 during cpu hotplug

On Wed, Sep 17, 2014 at 03:17:52PM +0800, Wanpeng Li 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
> 
> This bug can be triggered by hot add and remove large number of xen
> domain0's vcpus repeatedly.
> 
> 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.
> 
> Reviewed-by: Toshi Kani <toshi.kani@...com>
> Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> Tested-by: Linn Crosetto <linn@...com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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