linux-kernel - Re: [PATCH] cpusets: rework guarantee_online_cpus() to fix deadlock with cpu

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Message-ID: <4A74F767.7060401@cn.fujitsu.com>
Date:	Sun, 02 Aug 2009 10:18:15 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, Li Zefan <lizf@...fujitsu.com>,
	Miao Xie <miaox@...fujitsu.com>,
	Paul Menage <menage@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: Re: [PATCH] cpusets: rework guarantee_online_cpus() to fix deadlock
 with cpu_down()

Oleg Nesterov wrote:

> 
> 	- do NOT scan cs->parent cpusets. If there are no online CPUs in
> 	  cs->cpus_allowed, we use cpu_online_mask. This is only possible
> 	  when we are called by cpu_down() hooks, in that case
> 	  cpuset_track_online_cpus(CPU_DEAD) will fix things later.
> 


We must scan cs->parent cpusets.
A task is constrained by a cpuset, it must be constrained
this cpuset's parent too.

cpuset_lock() is not awful at all.

Lai.


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