linux-kernel - Re: [PATCH] cpusets: fix deadlock with cpu_down()->cpuset

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Message-ID: <20090729230043.GA28175@redhat.com>
Date:	Thu, 30 Jul 2009 01:00:43 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Cc:	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: fix deadlock with cpu_down()->cpuset_lock()

On 07/29, Oleg Nesterov wrote:
>
> I strongly believe the bug does exist, but this patch needs the review
> from maintainers.

Yes...

> IOW, with this patch migration_call(CPU_DEAD) runs without callback_mutex,
> but kernel/cpuset.c always takes get_online_cpus() before callback_mutex.

Oh. I'm afraid this is not an option.

callback_mutex should nest under cgroup_mutex, but cpu hotplu pathes
take cgroup_mutex under cpu_hotplug->lock. Lockdep won't be happy.

Oleg.

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