Re: [PATCH RFC] stop_machine: make stop_machine safe and efficientto call early

[Tejun Heo]

Hello, Jeremy.

On Fri, Sep 30, 2011 at 09:28:15AM -0700, Jeremy Fitzhardinge wrote:
> Make stop_machine() safe to call early in boot, before SMP has been
> set up, by simply calling the callback function directly if there's
> only one CPU online.
...
> @@ -485,6 +485,9 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
>  					    .num_threads = num_online_cpus(),
>  					    .active_cpus = cpus };
>  
> +	if (smdata.num_threads == 1)
> +		return (*fn)(data);
> +

As others have pointed out, you'll need to call both local and hardirq
disables.  Also, I think the description and the code are a bit
misleading.  How aobut setting cpu_stop_initialized in cpu_stop_init()
and testing it from __stop_machine() instead?  I think it would be
better to keep the behavior as uniform as possible once things are up
and running.

Thank you.

-- 
tejun
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