cpu/hotplug: Move bringup of secondary CPUs out of smp_init()

This is the last direct user of cpu_up() before it can become an internal
implementation detail of the cpu subsystem.

Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200323135110.30522-17-qais.yousef@arm.com

include/linux/cpu.h

@@ -94,6 +94,7 @@ void notify_cpu_starting(unsigned int cpu);
 extern void cpu_maps_update_begin(void);
 extern void cpu_maps_update_done(void);
 int bringup_hibernate_cpu(unsigned int sleep_cpu);
+void bringup_nonboot_cpus(unsigned int setup_max_cpus);
 
 #else	/* CONFIG_SMP */
 #define cpuhp_tasks_frozen	0

kernel/cpu.c

@@ -1298,6 +1298,18 @@ int bringup_hibernate_cpu(unsigned int sleep_cpu)
 	return 0;
 }
 
+void bringup_nonboot_cpus(unsigned int setup_max_cpus)
+{
+	unsigned int cpu;
+
+	for_each_present_cpu(cpu) {
+		if (num_online_cpus() >= setup_max_cpus)
+			break;
+		if (!cpu_online(cpu))
+			cpu_up(cpu);
+	}
+}
+
 #ifdef CONFIG_PM_SLEEP_SMP
 static cpumask_var_t frozen_cpus;
 

kernel/smp.c

@@ -597,20 +597,13 @@ void __init setup_nr_cpu_ids(void)
 void __init smp_init(void)
 {
 	int num_nodes, num_cpus;
-	unsigned int cpu;
 
 	idle_threads_init();
 	cpuhp_threads_init();
 
 	pr_info("Bringing up secondary CPUs ...\n");
 
-	/* FIXME: This should be done in userspace --RR */
-	for_each_present_cpu(cpu) {
-		if (num_online_cpus() >= setup_max_cpus)
-			break;
-		if (!cpu_online(cpu))
-			cpu_up(cpu);
-	}
+	bringup_nonboot_cpus(setup_max_cpus);
 
 	num_nodes = num_online_nodes();
 	num_cpus  = num_online_cpus();