linux-kernel - Re: [Bugfix v2] sched: fix possible invalid memory access caused by CPU hot-addition

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Date:	Wed, 30 Apr 2014 12:26:37 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [Bugfix v2] sched: fix possible invalid memory access caused
 by CPU hot-addition

Thanks Peter, I will try to find other solutions.

On 2014/4/28 15:09, Peter Zijlstra wrote:
> On Mon, Apr 28, 2014 at 10:48:13AM +0800, Jiang Liu wrote:
>> Intel platforms with Nehalem/Westmere/IvyBridge CPUs may support socket
>> hotplug/online at runtime. The CPU hot-addition flow is:
>> 1) handle CPU hot-addition event
>> 	1.a) gather platform specific information
>> 	1.b) associate hot-added CPU with NUMA node
>> 	1.c) create CPU device
>> 2) online hot-added CPU through sysfs:
>> 	2.a)	cpu_up()
>> 	2.b)		->try_online_node()
>> 	2.c)			->hotadd_new_pgdat()
>> 	2.d)			->node_set_online()
>>
>> Between 1.b and 2.c, hot-added CPUs are associated with NUMA nodes
>> but those NUMA nodes may still be in offlined state. So we should
>> check node_online(nid) before calling kmalloc_node(nid) and friends,
>> otherwise it may cause invalid memory access as below.
> 
> So complete and full NAK on this. This is a workaround for a fucked in
> the head BIOS. If you're going to do a work around for that they should
> live in arch/ space, not in core code.
> 
> The code in question is nearly 7 years old (2.6.24), which leads me to
> believe it works just fine for (regular) memory less nodes as I've not
> had complaints about it before.
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