kernel/printk: Convert to hotplug state machine

Install the callbacks via the state machine.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20161103145021.28528-3-bigeasy@linutronix.deSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/cpuhotplug.h

@@ -31,6 +31,7 @@ enum cpuhp_state {
 	CPUHP_S390_PFAULT_DEAD,
 	CPUHP_BLK_MQ_DEAD,
 	CPUHP_FS_BUFF_DEAD,
+	CPUHP_PRINTK_DEAD,
 	CPUHP_WORKQUEUE_PREP,
 	CPUHP_POWER_NUMA_PREPARE,
 	CPUHP_HRTIMERS_PREPARE,

kernel/printk/printk.c

@@ -2185,27 +2185,18 @@ void resume_console(void)
 
 /**
  * console_cpu_notify - print deferred console messages after CPU hotplug
- * @self: notifier struct
- * @action: CPU hotplug event
- * @hcpu: unused
+ * @cpu: unused
  *
  * If printk() is called from a CPU that is not online yet, the messages
  * will be spooled but will not show up on the console.  This function is
  * called when a new CPU comes online (or fails to come up), and ensures
  * that any such output gets printed.
  */
-static int console_cpu_notify(struct notifier_block *self,
-	unsigned long action, void *hcpu)
+static int console_cpu_notify(unsigned int cpu)
 {
-	switch (action) {
-	case CPU_ONLINE:
-	case CPU_DEAD:
-	case CPU_DOWN_FAILED:
-	case CPU_UP_CANCELED:
 	console_lock();
 	console_unlock();
-	}
-	return NOTIFY_OK;
+	return 0;
 }
 
 /**
@@ -2843,6 +2834,7 @@ EXPORT_SYMBOL(unregister_console);
 static int __init printk_late_init(void)
 {
 	struct console *con;
+	int ret;
 
 	for_each_console(con) {
 		if (!keep_bootcon && con->flags & CON_BOOT) {
@@ -2857,7 +2849,12 @@ static int __init printk_late_init(void)
 				unregister_console(con);
 		}
 	}
-	hotcpu_notifier(console_cpu_notify, 0);
+	ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
+					console_cpu_notify);
+	WARN_ON(ret < 0);
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
+					console_cpu_notify, NULL);
+	WARN_ON(ret < 0);
 	return 0;
 }
 late_initcall(printk_late_init);