[PATCH 01/14] xfs: introduce CPU hotplug infrastructure

["Darrick J. Wong" <djwong@xxxxxxxxxx>]

From: Dave Chinner <dchinner@xxxxxxxxxx>

We need to move to per-cpu state for both deferred inode
inactivation and 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, we only need CPU dead notifications, so we only set
up a callback for these notifications. The infrastructure can be
updated in future for other CPU hotplug state machine notifications
easily if ever needed.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
[djwong: rearrange some macros, fix function prototypes]
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
 fs/xfs/xfs_super.c         |   42 +++++++++++++++++++++++++++++++++++++++++-
 include/linux/cpuhotplug.h |    1 +
 2 files changed, 42 insertions(+), 1 deletion(-)


diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 36fc81e52dc2..d47fac7c8afd 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -2111,6 +2111,39 @@ xfs_destroy_workqueues(void)
 	destroy_workqueue(xfs_alloc_wq);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+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);
+}
+
+#else /* !CONFIG_HOTPLUG_CPU */
+static inline int xfs_cpu_hotplug_init(void) { return 0; }
+static inline void xfs_cpu_hotplug_destroy(void) {}
+#endif
+
 STATIC int __init
 init_xfs_fs(void)
 {
@@ -2123,9 +2156,13 @@ init_xfs_fs(void)
 
 	xfs_dir_startup();
 
+	error = xfs_cpu_hotplug_init();
+	if (error)
+		goto out;
+
 	error = xfs_init_zones();
 	if (error)
-		goto out;
+		goto out_destroy_hp;
 
 	error = xfs_init_workqueues();
 	if (error)
@@ -2206,6 +2243,8 @@ init_xfs_fs(void)
 	xfs_destroy_workqueues();
  out_destroy_zones:
 	xfs_destroy_zones();
+ out_destroy_hp:
+	xfs_cpu_hotplug_destroy();
  out:
 	return error;
 }
@@ -2228,6 +2267,7 @@ 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 f39b34b13871..439adc05be4e 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,