Re: [PATCH 10/43] stop_machine: reimplement without using workqueue

From: Tejun Heo
Date: Mon Mar 01 2010 - 11:28:44 EST


On 03/02/2010 12:37 AM, Oleg Nesterov wrote:
>> Hmmm... I'm probably missing something but I don't see how
>> stop_machine_cpu_callback(CPU_POST_DEAD) depends on stop_cpu() thread
>> already parked in schedule(). Can you elaborate a bit?
> Suppose that, when stop_machine_cpu_callback(CPU_POST_DEAD) is called,
> that stop_cpu() thread T is still running and it is going to check state
> before schedule().
> CPU_POST_DEAD is called after cpu_hotplug_done(), another CPU can do
> stop_machine() and set STOPMACHINE_PREPARE.
> If T sees state == STOPMACHINE_PREPARE it will join the game, but it
> wasn't counted in thread_ack counter, it is not cpu-bound, etc.

Oh, I see. I was thinking get/put_online_cpus() block is exclusive
against cpu_maps_update_begin/done() instead of
cpu_hotplug_begin/done(). Will update and add comments.


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