stop_machine: make stop_machine safe and efficient to call early
Make stop_machine() safe to call early in boot, before stop_machine()
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> Acked-by: Tejun Heo <tj@kernel.org> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> 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>