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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@linux.intel.com>
Organization: Intel
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To: Peter Zijlstra <peterz@infradead.org>
CC: Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Tony Luck <tony.luck@intel.com>, linux-kernel@vger.kernel.org
Subject: Re: [Bugfix] sched: fix possible invalid memory access caused by
 CPU hot-addition
References: <1398144435-26271-1-git-send-email-jiang.liu@linux.intel.com> <20140422081515.GF11182@twins.programming.kicks-ass.net>
In-Reply-To: <20140422081515.GF11182@twins.programming.kicks-ass.net>
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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? 
>