[PATCH 1/2] xfs: introduce CPU hotplug infrastructure

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

We need to move to per-cpu state for CIL tracking, but to do that we
need to handle CPUs being removed from the system by the hot-plug
code. Introduce generic XFS infrastructure to handle CPU hotplug
events that is set up at module init time and torn down at module
exit time.

Initially, the CIL only needs CPU dead notifications, so we only set
up a callback for these notifications. The infrastructure can be
updated in future for CPU add notifications easily if every needed.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/xfs_super.c         | 38 +++++++++++++++++++++++++++++++++++++-
 include/linux/cpuhotplug.h |  1 +
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 017ba9c24c2d..0146d3c89da9 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -2123,6 +2123,35 @@ xfs_destroy_workqueues(void)
 	destroy_workqueue(xfs_alloc_wq);
 }
 
+static int
+xfs_cpu_dead(
+	unsigned int		cpu)
+{
+	return 0;
+}
+
+static int __init
+xfs_cpu_hotplug_init(void)
+{
+	int	error;
+
+	error = cpuhp_setup_state_nocalls(CPUHP_XFS_DEAD,
+					"xfs:dead", NULL,
+					xfs_cpu_dead);
+	if (error < 0) {
+		xfs_alert(NULL,
+"Failed to initialise CPU hotplug, error %d. XFS is non-functional.",
+			error);
+	}
+	return error;
+}
+
+static void
+xfs_cpu_hotplug_destroy(void)
+{
+	cpuhp_remove_state_nocalls(CPUHP_XFS_DEAD);
+}
+
 STATIC int __init
 init_xfs_fs(void)
 {
@@ -2135,10 +2164,14 @@ init_xfs_fs(void)
 
 	xfs_dir_startup();
 
-	error = xfs_init_zones();
+	error = xfs_cpu_hotplug_init();
 	if (error)
 		goto out;
 
+	error = xfs_init_zones();
+	if (error)
+		goto out_destroy_hp;
+
 	error = xfs_init_workqueues();
 	if (error)
 		goto out_destroy_zones;
@@ -2218,6 +2251,8 @@ init_xfs_fs(void)
 	xfs_destroy_workqueues();
  out_destroy_zones:
 	xfs_destroy_zones();
+ out_destroy_hp:
+	xfs_cpu_hotplug_destroy();
  out:
 	return error;
 }
@@ -2240,6 +2275,7 @@ exit_xfs_fs(void)
 	xfs_destroy_workqueues();
 	xfs_destroy_zones();
 	xfs_uuid_table_free();
+	xfs_cpu_hotplug_destroy();
 }
 
 module_init(init_xfs_fs);
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 4a62b3980642..bf8f29ad9bf8 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -52,6 +52,7 @@ enum cpuhp_state {
 	CPUHP_FS_BUFF_DEAD,
 	CPUHP_PRINTK_DEAD,
 	CPUHP_MM_MEMCQ_DEAD,
+	CPUHP_XFS_DEAD,
 	CPUHP_PERCPU_CNT_DEAD,
 	CPUHP_RADIX_DEAD,
 	CPUHP_PAGE_ALLOC_DEAD,