kernel: remove stop_machine() Kconfig dependency

kernel: remove stop_machine() Kconfig dependency

Currently the full stop_machine() routine is only enabled on SMP if
module unloading is enabled, or if the CPUs are hotpluggable.  This
leads to configurations where stop_machine() is broken as it will then
only run the callback on the local CPU with irqs disabled, and not stop
the other CPUs or run the callback on them.

For example, this breaks MTRR setup on x86 in certain configs since
ea8596bb2d8d379 ("kprobes/x86: Remove unused text_poke_smp() and
text_poke_smp_batch() functions") as the MTRR is only established on the
boot CPU.

This patch removes the Kconfig option for STOP_MACHINE and uses the SMP
and HOTPLUG_CPU config options to compile the correct stop_machine() for
the architecture, removing the false dependency on MODULE_UNLOAD in the
process.

Link: https://lkml.org/lkml/2014/10/8/124
References: https://bugs.freedesktop.org/show_bug.cgi?id=84794
Signed-off-by: Chris Wilson <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Pranith Kumar <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Iulia Manda <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Chuck Ebbert <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>