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

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Message-ID: <4A77E4D0.20900@cn.fujitsu.com>
Date:	Tue, 04 Aug 2009 15:35:44 +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:
> On 08/02, Lai Jiangshan wrote:
>> 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,
> 
> Yes, the task esacpes its cpuset. With or without this patch.
> Because cs->cpus_allowed has no online CPUs.
> 
>> it must be constrained
>> this cpuset's parent too.
> 
> It will be constained again, after scan_for_empty_cpusets(), no?

cpuset_cpus_allowed() is not only  used for CPU offline.

sched_setaffinity() also uses it. The task will not be constained again.
Or I missed something.

Lai

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