Re: [Xen-devel] [PATCH RFC V2 2/5] stop_machine: make stop_machine safe and efficient to call early

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Sat, Oct 01, 2011 at 02:55:34PM -0700, Jeremy Fitzhardinge wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> 
> 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.
> 
> [ Fixes from AKPM:
>    - add comment
>    - local_irq_flags, not save_flags
>    - also call hard_irq_disable() for systems which need it
> 
>   Tejun suggested using an explicit flag rather than just looking at
>   the online cpu count. ]
> 
> 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>
> ---
>  kernel/stop_machine.c |   21 +++++++++++++++++++++
>  1 files changed, 21 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> index ba5070c..9c59d9e 100644
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -41,6 +41,7 @@ struct cpu_stopper {
>  };
>  
>  static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
> +static bool stop_machine_initialized = false;

__read_mostly?

Thought it probably does not really matter that much in what section it
is put in.