Re: [PATCH 2/4] stop_machine: reimplement using cpuhog

[Tejun Heo <tj@kernel.org>]

Hello,

On 03/09/2010 04:06 AM, Oleg Nesterov wrote:
> On 03/09, Tejun Heo wrote:
>>
>>  int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
>>  {
>> ...
>> +	/* Set the initial state and hog all online cpus. */
>> +	set_state(&smdata, STOPMACHINE_PREPARE);
>> +	return hog_cpus(cpu_online_mask, stop_cpu, &smdata);
>>  }
> 
> Could you please confirm this is correct?
> 
> I am not sure I understand how the code looks with the patch applied,
> but the lockless set_state() above can confuse another stop_machine()
> in progress?

set_state() now modifies smdata->state and smdata is now local
variable of __stop_machine().  stop_machine instances don't have any
shared resource anymore.  Synchronization and resource sharing are all
cpuhog's responsibilities.

Thanks.

-- 
tejun