[PATCH RFC 08/10] xfs: Introduce xfs_fs_destroy_super()

[Kirill Tkhai]

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 <ktk...@virtuozzo.com>
---
 fs/xfs/xfs_super.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 9e2ce4cd98e1..c1e00dd06893 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1774,11 +1774,20 @@ xfs_fs_put_super(
        xfs_destroy_mount_workqueues(mp);
        xfs_close_devices(mp);
 
-       sb->s_fs_info = NULL;
        xfs_free_fsname(mp);
-       kfree(mp);
 }
 
+STATIC void
+xfs_fs_destroy_super(
+       struct super_block      *sb)
+{
+       if (sb->s_fs_info) {
+               kfree(sb->s_fs_info);
+               sb->s_fs_info = NULL;
+       }
+}
+
+
 STATIC struct dentry *
 xfs_fs_mount(
        struct file_system_type *fs_type,
@@ -1816,6 +1825,7 @@ 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,