linux-kernel - Re: [PATCH] cpu_hotplug: don't affect current task's affinity

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Message-ID: <4A67C5BB.3070302@cn.fujitsu.com>
Date:	Thu, 23 Jul 2009 10:06:51 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] cpu_hotplug: don't affect current task's affinity

Andrew Morton wrote:

> 
> Or are you saying that the mask _should_ have been 0-1,3 but the kernel
> incorrectly set it to "0"?
> 

Yes, the mask should become 0-1,3. when original is 2 after cpu2 is offlined.

When cpu2 is offined

original mask			after cpu2 is offined
1				1
1-2				1
0-3				0-1,3
2				0-1,3
2(the task who do the offline)  0

I think the last line is incorrect. This patch fix it.


> 
> Also, it says "The recovery of the current tasks's cpus_allowed will
> fail under some conditions".  What are those conditions?
> 

A condition is described in changelog(the same as above).

An example of other condition: the CPUSET of the task is changed
when this task do the offline... the last recovery may fails.

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