adfs: delayed freeing of sbi

makes ->d_hash() and ->d_compare() safety in RCU mode independent
from vfsmount_lock.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/adfs/adfs.h

@@ -43,9 +43,12 @@ struct adfs_dir_ops;
  * ADFS file system superblock data in memory
  */
 struct adfs_sb_info {
-	struct adfs_discmap *s_map;	/* bh list containing map		 */
-	struct adfs_dir_ops *s_dir;	/* directory operations			 */
-
+	union { struct {
+		struct adfs_discmap *s_map;	/* bh list containing map	 */
+		struct adfs_dir_ops *s_dir;	/* directory operations		 */
+		};
+		struct rcu_head rcu;		/* used only at shutdown time	 */
+	};
 	kuid_t		s_uid;		/* owner uid				 */
 	kgid_t		s_gid;		/* owner gid				 */
 	umode_t		s_owner_mask;	/* ADFS owner perm -> unix perm		 */

fs/adfs/super.c

@@ -123,8 +123,7 @@ static void adfs_put_super(struct super_block *sb)
 	for (i = 0; i < asb->s_map_size; i++)
 		brelse(asb->s_map[i].dm_bh);
 	kfree(asb->s_map);
-	kfree(asb);
-	sb->s_fs_info = NULL;
+	kfree_rcu(asb, rcu);
 }
 
 static int adfs_show_options(struct seq_file *seq, struct dentry *root)