diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 849b8c767efb6295c41102e3018bfdd901cc3dd8..982152d3f9200c92334da084ddf9baa90196696c 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1460,8 +1460,8 @@ int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
  * callers (such as fiemap) which want to know whether the extent is
  * shared but do not need a ref count.
  *
- * This attempts to allocate a transaction in order to account for
- * delayed refs, but continues on even when the alloc fails.
+ * This attempts to attach to the running transaction in order to account for
+ * delayed refs, but continues on even when no running transaction exists.
  *
  * Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
  */
@@ -1484,13 +1484,16 @@ int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr)
 	tmp = ulist_alloc(GFP_NOFS);
 	roots = ulist_alloc(GFP_NOFS);
 	if (!tmp || !roots) {
-		ulist_free(tmp);
-		ulist_free(roots);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto out;
 	}
 
-	trans = btrfs_join_transaction(root);
+	trans = btrfs_attach_transaction(root);
 	if (IS_ERR(trans)) {
+		if (PTR_ERR(trans) != -ENOENT && PTR_ERR(trans) != -EROFS) {
+			ret = PTR_ERR(trans);
+			goto out;
+		}
 		trans = NULL;
 		down_read(&fs_info->commit_root_sem);
 	} else {
@@ -1523,6 +1526,7 @@ int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr)
 	} else {
 		up_read(&fs_info->commit_root_sem);
 	}
+out:
 	ulist_free(tmp);
 	ulist_free(roots);
 	return ret;