cpu/hotplug: Initialise all cpuhp_cpu_state structs earlier

Rather than waiting until a CPU is first brought online, do the
initialisation of the cpuhp_cpu_state structure for each CPU during the
__init phase. This saves a (small) amount of non-__init memory and
avoids potential confusion about when the cpuhp_cpu_state struct is
valid.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220411152233.474129-3-steven.price@arm.com

kernel/cpu.c

@@ -716,14 +716,6 @@ static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
 /*
  * The cpu hotplug threads manage the bringup and teardown of the cpus
  */
-static void cpuhp_create(unsigned int cpu)
-{
-	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
-
-	init_completion(&st->done_up);
-	init_completion(&st->done_down);
-}
-
 static int cpuhp_should_run(unsigned int cpu)
 {
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
@@ -883,15 +875,27 @@ static int cpuhp_kick_ap_work(unsigned int cpu)
 
 static struct smp_hotplug_thread cpuhp_threads = {
 	.store			= &cpuhp_state.thread,
-	.create			= &cpuhp_create,
 	.thread_should_run	= cpuhp_should_run,
 	.thread_fn		= cpuhp_thread_fun,
 	.thread_comm		= "cpuhp/%u",
 	.selfparking		= true,
 };
 
+static __init void cpuhp_init_state(void)
+{
+	struct cpuhp_cpu_state *st;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		st = per_cpu_ptr(&cpuhp_state, cpu);
+		init_completion(&st->done_up);
+		init_completion(&st->done_down);
+	}
+}
+
 void __init cpuhp_threads_init(void)
 {
+	cpuhp_init_state();
 	BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
 	kthread_unpark(this_cpu_read(cpuhp_state.thread));
 }