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>

3 files changed, 68 insertions, 7 deletions

diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 0e552e72a4c4..6b524a0d02e4 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -6,8 +6,6 @@
 #include <linux/list.h>
 #include <asm/system.h>
 
-#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
-
 /*
  * stop_cpu[s]() is simplistic per-cpu maximum priority cpu
  * monopolization mechanism.  The caller can specify a non-sleeping
@@ -18,9 +16,10 @@
  * up and requests are guaranteed to be served as long as the target
  * cpus are online.
  */
-
 typedef int (*cpu_stop_fn_t)(void *arg);
 
+#ifdef CONFIG_SMP
+
 struct cpu_stop_work {
         struct list_head        list;           /* cpu_stopper->works */
         cpu_stop_fn_t           fn;
@@ -34,12 +33,70 @@ void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg);
 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg);
 
+#else   /* CONFIG_SMP */
+
+#include <linux/workqueue.h>
+
+struct cpu_stop_work {
+        struct work_struct      work;
+        cpu_stop_fn_t           fn;
+        void                    *arg;
+};
+
+static inline int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
+{
+        int ret = -ENOENT;
+        preempt_disable();
+        if (cpu == smp_processor_id())
+                ret = fn(arg);
+        preempt_enable();
+        return ret;
+}
+
+static void stop_one_cpu_nowait_workfn(struct work_struct *work)
+{
+        struct cpu_stop_work *stwork =
+                container_of(work, struct cpu_stop_work, work);
+        preempt_disable();
+        stwork->fn(stwork->arg);
+        preempt_enable();
+}
+
+static inline void stop_one_cpu_nowait(unsigned int cpu,
+                                       cpu_stop_fn_t fn, void *arg,
+                                       struct cpu_stop_work *work_buf)
+{
+        if (cpu == smp_processor_id()) {
+                INIT_WORK(&work_buf->work, stop_one_cpu_nowait_workfn);
+                work_buf->fn = fn;
+                work_buf->arg = arg;
+                schedule_work(&work_buf->work);
+        }
+}
+
+static inline int stop_cpus(const struct cpumask *cpumask,
+                            cpu_stop_fn_t fn, void *arg)
+{
+        if (cpumask_test_cpu(raw_smp_processor_id(), cpumask))
+                return stop_one_cpu(raw_smp_processor_id(), fn, arg);
+        return -ENOENT;
+}
+
+static inline int try_stop_cpus(const struct cpumask *cpumask,
+                                cpu_stop_fn_t fn, void *arg)
+{
+        return stop_cpus(cpumask, fn, arg);
+}
+
+#endif  /* CONFIG_SMP */
+
 /*
  * stop_machine "Bogolock": stop the entire machine, disable
  * interrupts.  This is a very heavy lock, which is equivalent to
  * grabbing every spinlock (and more).  So the "read" side to such a
  * lock is anything which disables preeempt.
  */
+#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
 
 /**
  * stop_machine: freeze the machine on all CPUs and run this function
@@ -67,7 +124,7 @@ int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus);
  */
 int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus);
 
-#else
+#else    /* CONFIG_STOP_MACHINE && CONFIG_SMP */
 
 static inline int stop_machine(int (*fn)(void *), void *data,
                                const struct cpumask *cpus)
@@ -79,5 +136,5 @@ static inline int stop_machine(int (*fn)(void *), void *data,
         return ret;
 }
 
-#endif /* CONFIG_SMP */
-#endif /* _LINUX_STOP_MACHINE */
+#endif  /* CONFIG_STOP_MACHINE && CONFIG_SMP */
+#endif  /* _LINUX_STOP_MACHINE */
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 */