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Message-ID: <54F52ACF.4030103@huawei.com>
Date: Tue, 3 Mar 2015 11:30:23 +0800
From: Xishi Qiu <qiuxishi@huawei.com>
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Subject: node-hotplug: is memset 0 safe in try_offline_node()?
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To: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>, Andrew Morton <akpm@linux-foundation.org>, Tang Chen <tangchen@cn.fujitsu.com>, Yinghai Lu <yinghai@kernel.org>
Cc: Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, Toshi Kani <toshi.kani@hp.com>, Mel Gorman <mgorman@suse.de>, Tejun Heo <tj@kernel.org>

When hot-remove a numa node, we will clear pgdat,
but is memset 0 safe in try_offline_node()?

process A:			offline node XX:
for_each_populated_zone()
find online node XX
cond_resched()
				offline cpu and memory, then try_offline_node()
				node_set_offline(nid), and memset(pgdat, 0, sizeof(*pgdat))
access node XX's pgdat
NULL pointer access error

Thanks,
Xishi Qiu

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Date: Tue, 3 Mar 2015 11:30:23 +0800
From: Xishi Qiu <qiuxishi@huawei.com>
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To: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tang Chen <tangchen@cn.fujitsu.com>, Yinghai Lu <yinghai@kernel.org>
CC: Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        "Toshi Kani" <toshi.kani@hp.com>, Mel Gorman <mgorman@suse.de>,
        Tejun Heo <tj@kernel.org>
Subject: node-hotplug: is memset 0 safe in try_offline_node()?
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When hot-remove a numa node, we will clear pgdat,
but is memset 0 safe in try_offline_node()?

process A:			offline node XX:
for_each_populated_zone()
find online node XX
cond_resched()
				offline cpu and memory, then try_offline_node()
				node_set_offline(nid), and memset(pgdat, 0, sizeof(*pgdat))
access node XX's pgdat
NULL pointer access error

Thanks,
Xishi Qiu