btrfs: preparation to fixing mount/umount race

We need fs_info and root to live until the moment when the victim
superblock leaves the list, so we need to postpone free_fs_info()
until after ->put_super().  The call is buried in close_ctree(),
though, so we need to lift it into the callers (including
btrfs_put_super()) first.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/btrfs/disk-io.c

@@ -2424,6 +2424,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 		up_read(&fs_info->cleanup_work_sem);
 		if (err) {
 			close_ctree(tree_root);
+			free_fs_info(fs_info);
 			return ERR_PTR(err);
 		}
 	}
@@ -3059,8 +3060,6 @@ int close_ctree(struct btrfs_root *root)
 	bdi_destroy(&fs_info->bdi);
 	cleanup_srcu_struct(&fs_info->subvol_srcu);
 
-	free_fs_info(fs_info);
-
 	return 0;
 }
 

fs/btrfs/super.c

@@ -151,6 +151,7 @@ static void btrfs_put_super(struct super_block *sb)
 	int ret;
 
 	ret = close_ctree(root);
+	free_fs_info(root->fs_info);
 	sb->s_fs_info = NULL;
 
 	(void)ret; /* FIXME: need to fix VFS to return error? */
@@ -589,6 +590,7 @@ static int btrfs_fill_super(struct super_block *sb,
 	struct inode *inode;
 	struct dentry *root_dentry;
 	struct btrfs_root *tree_root;
+	struct btrfs_fs_info *fs_info;
 	struct btrfs_key key;
 	int err;
 
@@ -609,12 +611,13 @@ static int btrfs_fill_super(struct super_block *sb,
 		printk("btrfs: open_ctree failed\n");
 		return PTR_ERR(tree_root);
 	}
+	fs_info = tree_root->fs_info;
 	sb->s_fs_info = tree_root;
 
 	key.objectid = BTRFS_FIRST_FREE_OBJECTID;
 	key.type = BTRFS_INODE_ITEM_KEY;
 	key.offset = 0;
-	inode = btrfs_iget(sb, &key, tree_root->fs_info->fs_root, NULL);
+	inode = btrfs_iget(sb, &key, fs_info->fs_root, NULL);
 	if (IS_ERR(inode)) {
 		err = PTR_ERR(inode);
 		goto fail_close;
@@ -635,6 +638,7 @@ static int btrfs_fill_super(struct super_block *sb,
 
 fail_close:
 	close_ctree(tree_root);
+	free_fs_info(fs_info);
 	return err;
 }