linux-kernel - migrate_disable() race with cpu hotplug?

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Message-ID: <CAM2zO=AxRYEG=iJqrefOL34GW5ukoQKxYQdJ02mez=s5UZPoJg@mail.gmail.com>
Date:	Tue, 26 Jul 2011 16:59:48 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: migrate_disable() race with cpu hotplug?

When reading the code, I'm afraid there is a race between migrate_disable()
and cpu hotplug. A scenario will like below:

	CPU0			CPU1
_cpu_down();
  cpu_unplug_begin();
    wait_for_completion()
  			sync_unplug_thread();
			  complete();
			race_window? /*
				      * migrate_disable() will
				      * not take effect since
				      * hotplug is in progress
				      */

  __stop_machine();

I think it could happen but maybe I'm missing something.

Thanks,
Yong


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