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

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Message-ID: <53572939.7020509@linux.intel.com>
Date:	Wed, 23 Apr 2014 10:45:13 +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>, 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] sched: fix possible invalid memory access caused by
 CPU hot-addition

Hi Peter,
	It's not for memoryless node, but to solve a race window
in CPU hot-addition. The related CPU hot-addition flow is:
1) Handle CPU hot-addition event
1.a) gather platform specific information
1.b) associate hot-added CPU with a node
1.c) create CPU device
2) User online hot-added CPUs through sysfs:
2.a)	cpu_up()
2.b)		->try_online_node()
2.c)			->hotadd_new_pgdat()
2.d)			->node_set_online()

So between 1.b and 2.c, kmalloc_node(nid) may cause invalid
memory access without the node_online(nid) check.

Best Regards!
Gerry

On 2014/4/22 16:15, Peter Zijlstra wrote:
> On Tue, Apr 22, 2014 at 01:27:15PM +0800, Jiang Liu wrote:
>> When calling kzalloc_node(size, flags, node), we should first check
>> whether node is onlined, otherwise it may cause invalid memory access
>> as below.
> 
> But this is only for memory less node crap, right? 
> 
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