On Tue, 26 Jul 2011, Yong Zhang wrote:

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
				      */

Rightfully so. The caller will just block on the cpu_hotplug.lock
mutex until the unplug operation will be done.

Thanks,

	tglx