linux-kernel - Re: [PATCH v3 3/9] memory-hotplug: flush the work for the node when the node is offlined

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Date:	Fri, 19 Oct 2012 15:28:01 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	rientjes@...gle.com, liuj97@...il.com, len.brown@...el.com,
	benh@...nel.crashing.org, paulus@...ba.org, minchan.kim@...il.com,
	akpm@...ux-foundation.org, isimatu.yasuaki@...fujitsu.com
Subject: Re: [PATCH v3 3/9] memory-hotplug: flush the work for the node when
 the node is offlined

At 10/19/2012 03:01 PM, KOSAKI Motohiro Wrote:
> On Fri, Oct 19, 2012 at 2:46 AM,  <wency@...fujitsu.com> wrote:
>> From: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>>
>> If the node is onlined after it is offlined, we will clear the memory
>> to store the node's information. This structure contains struct work,
>> so we should flush work before the work's information is cleared.
> 
> This explanation is incorrect. Even if you don't call memset(), you should
> call flush_work() at offline event. Because of, after offlinining, we
> shouldn't touch any node data. Alive workqueue violate this principle.

Yes, I will update the description.

> 
> And, hmmm... Wait. Usually workqueue shutdowning has two phase. 1)
> inhibit enqueue new work 2) flush work. Otherwise other cpus may
> enqueue new work after flush_work(). Where is (1)?
> 


We schedule the work only when a memory section is onlined/offlined on this
node. When we come here, all the memory on this node has been offlined,
so we won't enqueue new work to this work. I will add a comment
to descript this.

Thanks
Wen Congyang


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