diff --git a/convert/main.c b/convert/main.c
index c9e50c036f92..73740fe26d55 100644
--- a/convert/main.c
+++ b/convert/main.c
@@ -1311,8 +1311,9 @@ static int do_convert(const char *devname, u32 convert_flags, u32 nodesize,
 		task_deinit(ctx.info);
 	}
 
-	image_root = btrfs_mksubvol(root, subvol_name,
-				    CONV_IMAGE_SUBVOL_OBJECTID, true);
+	image_root = btrfs_link_subvol(root, btrfs_root_dirid(&root->root_item),
+				       subvol_name,  CONV_IMAGE_SUBVOL_OBJECTID,
+				       true);
 	if (!image_root) {
 		error("unable to link subvolume %s", subvol_name);
 		goto fail;
diff --git a/kernel-shared/ctree.h b/kernel-shared/ctree.h
index bcf11d870061..a10a30e36b94 100644
--- a/kernel-shared/ctree.h
+++ b/kernel-shared/ctree.h
@@ -1230,8 +1230,9 @@ int btrfs_add_orphan_item(struct btrfs_trans_handle *trans,
 			  u64 ino);
 int btrfs_mkdir(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		char *name, int namelen, u64 parent_ino, u64 *ino, int mode);
-struct btrfs_root *btrfs_mksubvol(struct btrfs_root *root, const char *base,
-				  u64 root_objectid, bool convert);
+struct btrfs_root *btrfs_link_subvol(struct btrfs_root *root, u64 parent_ino,
+				     const char *name, u64 root_objectid,
+				     bool retry_suffix_names);
 int btrfs_find_free_objectid(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *fs_root,
 			     u64 dirid, u64 *objectid);
diff --git a/kernel-shared/inode.c b/kernel-shared/inode.c
index 50bb460acc79..ebb28b7666cc 100644
--- a/kernel-shared/inode.c
+++ b/kernel-shared/inode.c
@@ -601,11 +601,19 @@ out:
 	return ret;
 }
 
-struct btrfs_root *btrfs_mksubvol(struct btrfs_root *root,
-				  const char *base, u64 root_objectid,
-				  bool convert)
+/*
+ * Link a subvolume with @root_objectid to @parent_ino of @root, with the name
+ * @base.
+ *
+ * If @retry_suffix_names is true, and if there is already a dir item with the
+ * same name of @base, then it would retry with an increasing number as suffix,
+ * until a conflict-free name is found, or have tried too many times.
+ */
+struct btrfs_root *btrfs_link_subvol(struct btrfs_root *root, u64 parent_ino,
+				     const char *name, u64 root_objectid,
+				     bool retry_suffix_names)
 {
-	struct btrfs_trans_handle *trans;
+	struct btrfs_trans_handle *trans = NULL;
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct btrfs_root *tree_root = fs_info->tree_root;
 	struct btrfs_root *new_root = NULL;
@@ -613,32 +621,58 @@ struct btrfs_root *btrfs_mksubvol(struct btrfs_root *root,
 	struct btrfs_inode_item *inode_item;
 	struct extent_buffer *leaf;
 	struct btrfs_key key;
-	u64 dirid = btrfs_root_dirid(&root->root_item);
 	u64 index = 2;
 	char buf[BTRFS_NAME_LEN + 1]; /* for snprintf null */
 	int len;
 	int i;
 	int ret;
 
-	len = strlen(base);
-	if (len == 0 || len > BTRFS_NAME_LEN)
+	len = strlen(name);
+	if (len == 0 || len > BTRFS_NAME_LEN) {
+		error("invalid name length %u", len);
 		return NULL;
+	}
 
-	key.objectid = dirid;
+	/* Make sure @parent_ino of @root is a directory. */
+	key.objectid = parent_ino;
+	key.type = BTRFS_INODE_ITEM_KEY;
+	key.offset = 0;
+	ret = btrfs_lookup_inode(NULL, root, &path, &key, 0);
+	if (ret > 0) {
+		ret = -ENOENT;
+		/* Fallthrough */
+	}
+	if (ret < 0) {
+		errno = -ret;
+		error("failed to locate directory inode %llu of root %lld: %m",
+		      parent_ino, root->root_key.objectid);
+		goto fail;
+	}
+	inode_item = btrfs_item_ptr(path.nodes[0], path.slots[0],
+				    struct btrfs_inode_item);
+	if (!S_ISDIR(btrfs_inode_mode(path.nodes[0], inode_item))) {
+		ret = -EUCLEAN;
+		error("inode %llu of root %lld is not a directory",
+		      parent_ino, root->root_key.objectid);
+		goto fail;
+	}
+	btrfs_release_path(&path);
+
+	/* Locate one free dir index number. */
+	key.objectid = parent_ino;
 	key.type = BTRFS_DIR_INDEX_KEY;
 	key.offset = (u64)-1;
-
 	ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
 	if (ret <= 0) {
 		error("search for DIR_INDEX dirid %llu failed: %d",
-				(unsigned long long)dirid, ret);
+		      parent_ino, ret);
 		goto fail;
 	}
 
 	if (path.slots[0] > 0) {
 		path.slots[0]--;
 		btrfs_item_key_to_cpu(path.nodes[0], &key, path.slots[0]);
-		if (key.objectid == dirid && key.type == BTRFS_DIR_INDEX_KEY)
+		if (key.objectid == parent_ino && key.type == BTRFS_DIR_INDEX_KEY)
 			index = key.offset + 1;
 	}
 	btrfs_release_path(&path);
@@ -651,14 +685,14 @@ struct btrfs_root *btrfs_mksubvol(struct btrfs_root *root,
 		goto fail;
 	}
 
-	key.objectid = dirid;
+	key.objectid = parent_ino;
 	key.offset = 0;
 	key.type =  BTRFS_INODE_ITEM_KEY;
 
 	ret = btrfs_lookup_inode(trans, root, &path, &key, 1);
 	if (ret) {
 		error("search for INODE_ITEM %llu failed: %d",
-				(unsigned long long)dirid, ret);
+				parent_ino, ret);
 		goto fail;
 	}
 	leaf = path.nodes[0];
@@ -669,21 +703,21 @@ struct btrfs_root *btrfs_mksubvol(struct btrfs_root *root,
 	key.offset = (u64)-1;
 	key.type = BTRFS_ROOT_ITEM_KEY;
 
-	memcpy(buf, base, len);
-	if (convert) {
+	memcpy(buf, name, len);
+	if (retry_suffix_names) {
 		for (i = 0; i < 1024; i++) {
 			ret = btrfs_insert_dir_item(trans, root, buf, len,
-					dirid, &key, BTRFS_FT_DIR, index);
+					parent_ino, &key, BTRFS_FT_DIR, index);
 			if (ret != -EEXIST)
 				break;
-			len = snprintf(buf, ARRAY_SIZE(buf), "%s%d", base, i);
+			len = snprintf(buf, ARRAY_SIZE(buf), "%s%d", name, i);
 			if (len < 1 || len > BTRFS_NAME_LEN) {
 				ret = -EINVAL;
 				break;
 			}
 		}
 	} else {
-		ret = btrfs_insert_dir_item(trans, root, buf, len, dirid, &key,
+		ret = btrfs_insert_dir_item(trans, root, buf, len, parent_ino, &key,
 					    BTRFS_FT_DIR, index);
 	}
 	if (ret)
@@ -698,7 +732,7 @@ struct btrfs_root *btrfs_mksubvol(struct btrfs_root *root,
 	ret = btrfs_add_root_ref(trans, tree_root, root_objectid,
 				 BTRFS_ROOT_BACKREF_KEY,
 				 root->root_key.objectid,
-				 dirid, index, buf, len);
+				 parent_ino, index, buf, len);
 	if (ret) {
 		error("unable to add root backref for %llu: %d",
 				root->root_key.objectid, ret);
@@ -708,7 +742,7 @@ struct btrfs_root *btrfs_mksubvol(struct btrfs_root *root,
 	/* now add the forward ref */
 	ret = btrfs_add_root_ref(trans, tree_root, root->root_key.objectid,
 				 BTRFS_ROOT_REF_KEY, root_objectid,
-				 dirid, index, buf, len);
+				 parent_ino, index, buf, len);
 	if (ret) {
 		error("unable to add root ref for %llu: %d",
 				root->root_key.objectid, ret);
@@ -728,6 +762,8 @@ struct btrfs_root *btrfs_mksubvol(struct btrfs_root *root,
 		new_root = NULL;
 	}
 fail:
+	if (trans && ret < 0)
+		btrfs_abort_transaction(trans, ret);
 	return new_root;
 }
 
