[PATCH 6/8] xfs: introduce xfs_fs_destroy_super()

[Qi Zheng]

From: Kirill Tkhai <tkhai@xxxxx>

xfs_fs_nr_cached_objects() touches sb->s_fs_info,
and this patch makes it to be destructed later.

After this patch xfs_fs_nr_cached_objects() is safe
for splitting unregister_shrinker(): mp->m_perag_tree
is stable till destroy_super_work(), while iteration
over it is already RCU-protected by internal XFS
business.

Signed-off-by: Kirill Tkhai <tkhai@xxxxx>
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
 fs/xfs/xfs_super.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 7e706255f165..694616524c76 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -743,11 +743,18 @@ xfs_fs_drop_inode(
 }
 
 static void
-xfs_mount_free(
+xfs_free_names(
 	struct xfs_mount	*mp)
 {
 	kfree(mp->m_rtname);
 	kfree(mp->m_logname);
+}
+
+static void
+xfs_mount_free(
+	struct xfs_mount	*mp)
+{
+	xfs_free_names(mp);
 	kmem_free(mp);
 }
 
@@ -1136,8 +1143,19 @@ xfs_fs_put_super(
 	xfs_destroy_mount_workqueues(mp);
 	xfs_close_devices(mp);
 
-	sb->s_fs_info = NULL;
-	xfs_mount_free(mp);
+	xfs_free_names(mp);
+}
+
+static void
+xfs_fs_destroy_super(
+	struct super_block	*sb)
+{
+	if (sb->s_fs_info) {
+		struct xfs_mount	*mp = XFS_M(sb);
+
+		kmem_free(mp);
+		sb->s_fs_info = NULL;
+	}
 }
 
 static long
@@ -1165,6 +1183,7 @@ static const struct super_operations xfs_super_operations = {
 	.dirty_inode		= xfs_fs_dirty_inode,
 	.drop_inode		= xfs_fs_drop_inode,
 	.put_super		= xfs_fs_put_super,
+	.destroy_super		= xfs_fs_destroy_super,
 	.sync_fs		= xfs_fs_sync_fs,
 	.freeze_fs		= xfs_fs_freeze,
 	.unfreeze_fs		= xfs_fs_unfreeze,
-- 
2.30.2