hrtimer: Convert to hotplug state machine

Split out the clockevents callbacks instead of piggybacking them on
hrtimers.

This gets rid of a POST_DEAD user. See commit:

  54e88fad ("sched: Make sure timers have migrated before killing the migration_thread")

We just move the callback state to the proper place in the state machine.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160713153337.485419196@linutronix.deSigned-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/cpuhotplug.h

@@ -15,6 +15,7 @@ enum cpuhp_state {
 	CPUHP_X86_HPET_DEAD,
 	CPUHP_X86_APB_DEAD,
 	CPUHP_WORKQUEUE_PREP,
+	CPUHP_HRTIMERS_PREPARE,
 	CPUHP_NOTIFY_PREPARE,
 	CPUHP_BRINGUP_CPU,
 	CPUHP_AP_IDLE_DEAD,

include/linux/hrtimer.h

@@ -494,4 +494,11 @@ extern void __init hrtimers_init(void);
 /* Show pending timers: */
 extern void sysrq_timer_list_show(void);
 
+int hrtimers_prepare_cpu(unsigned int cpu);
+#ifdef CONFIG_HOTPLUG_CPU
+int hrtimers_dead_cpu(unsigned int cpu);
+#else
+#define hrtimers_dead_cpu	NULL
+#endif
+
 #endif

kernel/cpu.c

@@ -1190,6 +1190,11 @@ static struct cpuhp_step cpuhp_bp_states[] = {
 		.startup = workqueue_prepare_cpu,
 		.teardown = NULL,
 	},
+	[CPUHP_HRTIMERS_PREPARE] = {
+		.name = "hrtimers prepare",
+		.startup = hrtimers_prepare_cpu,
+		.teardown = hrtimers_dead_cpu,
+	},
 	/*
 	 * Preparatory and dead notifiers. Will be replaced once the notifiers
 	 * are converted to states.

kernel/time/hrtimer.c

@@ -1590,7 +1590,7 @@ SYSCALL_DEFINE2(nanosleep, struct timespec __user *, rqtp,
 /*
  * Functions related to boot-time initialization:
  */
-static void init_hrtimers_cpu(int cpu)
+int hrtimers_prepare_cpu(unsigned int cpu)
 {
 	struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);
 	int i;
@@ -1602,6 +1602,7 @@ static void init_hrtimers_cpu(int cpu)
 
 	cpu_base->cpu = cpu;
 	hrtimer_init_hres(cpu_base);
+	return 0;
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -1636,7 +1637,7 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 	}
 }
 
-static void migrate_hrtimers(int scpu)
+int hrtimers_dead_cpu(unsigned int scpu)
 {
 	struct hrtimer_cpu_base *old_base, *new_base;
 	int i;
@@ -1665,45 +1666,14 @@ static void migrate_hrtimers(int scpu)
 	/* Check, if we got expired work to do */
 	__hrtimer_peek_ahead_timers();
 	local_irq_enable();
+	return 0;
 }
 
 #endif /* CONFIG_HOTPLUG_CPU */
 
-static int hrtimer_cpu_notify(struct notifier_block *self,
-					unsigned long action, void *hcpu)
-{
-	int scpu = (long)hcpu;
-
-	switch (action) {
-
-	case CPU_UP_PREPARE:
-	case CPU_UP_PREPARE_FROZEN:
-		init_hrtimers_cpu(scpu);
-		break;
-
-#ifdef CONFIG_HOTPLUG_CPU
-	case CPU_DEAD:
-	case CPU_DEAD_FROZEN:
-		migrate_hrtimers(scpu);
-		break;
-#endif
-
-	default:
-		break;
-	}
-
-	return NOTIFY_OK;
-}
-
-static struct notifier_block hrtimers_nb = {
-	.notifier_call = hrtimer_cpu_notify,
-};
-
 void __init hrtimers_init(void)
 {
-	hrtimer_cpu_notify(&hrtimers_nb, (unsigned long)CPU_UP_PREPARE,
-			  (void *)(long)smp_processor_id());
-	register_cpu_notifier(&hrtimers_nb);
+	hrtimers_prepare_cpu(smp_processor_id());
 }
 
 /**