cpu_stop: add dummy implementation for UP

When !CONFIG_SMP, cpu_stop functions weren't defined at all which
could lead to build failures if UP code uses cpu_stop facility.  Add
dummy cpu_stop implementation for UP.  The waiting variants execute
the work function directly with preempt disabled and
stop_one_cpu_nowait() schedules a workqueue work.

Makefile and ifdefs around stop_machine implementation are updated to
accomodate CONFIG_SMP && !CONFIG_STOP_MACHINE case.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 5 insertions, 1 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index a987aa1676b5..149e18ef1ab1 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -68,7 +68,7 @@ obj-$(CONFIG_USER_NS) += user_namespace.o
 obj-$(CONFIG_PID_NS) += pid_namespace.o
 obj-$(CONFIG_IKCONFIG) += configs.o
 obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
-obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
+obj-$(CONFIG_SMP) += stop_machine.o
 obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
 obj-$(CONFIG_AUDIT) += audit.o auditfilter.o audit_watch.o
 obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 5b20141a5ec1..ef51d1fcf5e6 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -375,6 +375,8 @@ static int __init cpu_stop_init(void)
 }
 early_initcall(cpu_stop_init);
 
+#ifdef CONFIG_STOP_MACHINE
+
 /* This controls the threads on each CPU. */
 enum stopmachine_state {
         /* Dummy starting state for thread. */
@@ -477,3 +479,5 @@ int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
         return ret;
 }
 EXPORT_SYMBOL_GPL(stop_machine);
+
+#endif  /* CONFIG_STOP_MACHINE */