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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Date: Fri, 19 Oct 2012 14:33:17 -0400
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Subject: Re: [PATCH 1/10] memory-hotplug : check whether memory is offline or
 not when removing memory
To: Wen Congyang <wencongyang@gmail.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>,
        Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>, x86@kernel.org,
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        linuxppc-dev@lists.ozlabs.org, linux-acpi@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
        linux-ia64@vger.kernel.org, cmetcalf@tilera.com,
        sparclinux@vger.kernel.org, rientjes@google.com, liuj97@gmail.com,
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> I think it again, and found that this check is necessary. Because we only
> lock memory hotplug when offlining pages. Here is the steps to offline and
> remove memory:
>
> 1. lock memory hotplug
> 2. offline a memory section
> 3. unlock memory hotplug
> 4. repeat 1-3 to offline all memory sections
> 5. lock memory hotplug
> 6. remove memory
> 7. unlock memory hotplug
>
> All memory sections must be offlined before removing memory. But we don't
> hold
> the lock in the whole operation. So we should check whether all memory
> sections
> are offlined before step6.

You should describe the race scenario in the patch description. OK?
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