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

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 2011-09-30 at 09:28 -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.
> 
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: H. Peter Anvin <hpa@linux.intel.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> 
> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> index ba5070c..2df15ca 100644
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -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);

Doesn't interrupts need to be disabled here too? As stop machine
functions also guarantee that they will not be interrupted by
interrupts.

-- Steve

> +
>  	/* Set the initial state and stop all online cpus. */
>  	set_state(&smdata, STOPMACHINE_PREPARE);
>  	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
>