fs/buffer: 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: linux-fsdevel@vger.kernel.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20161103145021.28528-2-bigeasy@linutronix.deSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

fs/buffer.c

@@ -3403,7 +3403,7 @@ void free_buffer_head(struct buffer_head *bh)
 }
 EXPORT_SYMBOL(free_buffer_head);
 
-static void buffer_exit_cpu(int cpu)
+static int buffer_exit_cpu_dead(unsigned int cpu)
 {
 	int i;
 	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
@@ -3414,14 +3414,7 @@ static void buffer_exit_cpu(int cpu)
 	}
 	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
 	per_cpu(bh_accounting, cpu).nr = 0;
-}
-
-static int buffer_cpu_notify(struct notifier_block *self,
-			      unsigned long action, void *hcpu)
-{
-	if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
-		buffer_exit_cpu((unsigned long)hcpu);
-	return NOTIFY_OK;
+	return 0;
 }
 
 /**
@@ -3471,6 +3464,7 @@ EXPORT_SYMBOL(bh_submit_read);
 void __init buffer_init(void)
 {
 	unsigned long nrpages;
+	int ret;
 
 	bh_cachep = kmem_cache_create("buffer_head",
 			sizeof(struct buffer_head), 0,
@@ -3483,5 +3477,7 @@ void __init buffer_init(void)
 	 */
 	nrpages = (nr_free_buffer_pages() * 10) / 100;
 	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
-	hotcpu_notifier(buffer_cpu_notify, 0);
+	ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
+					NULL, buffer_exit_cpu_dead);
+	WARN_ON(ret < 0);
 }

include/linux/cpuhotplug.h

@@ -30,6 +30,7 @@ enum cpuhp_state {
 	CPUHP_ACPI_CPUDRV_DEAD,
 	CPUHP_S390_PFAULT_DEAD,
 	CPUHP_BLK_MQ_DEAD,
+	CPUHP_FS_BUFF_DEAD,
 	CPUHP_WORKQUEUE_PREP,
 	CPUHP_POWER_NUMA_PREPARE,
 	CPUHP_HRTIMERS_PREPARE,