1 files changed, 24 insertions, 14 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 11459fe84a29..982152d3f920 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -791,7 +791,7 @@ static int add_delayed_refs(const struct btrfs_fs_info *fs_info,
 			count = node->ref_mod * -1;
 			break;
 		default:
-			BUG_ON(1);
+			BUG();
 		}
 		*total_refs += count;
 		switch (node->type) {
@@ -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;
@@ -1747,7 +1751,7 @@ int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
 		else if (flags & BTRFS_EXTENT_FLAG_DATA)
 			*flags_ret = BTRFS_EXTENT_FLAG_DATA;
 		else
-			BUG_ON(1);
+			BUG();
 		return 0;
 	}
 
@@ -1912,13 +1916,19 @@ int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
 			extent_item_objectid);
 
 	if (!search_commit_root) {
-		trans = btrfs_join_transaction(fs_info->extent_root);
-		if (IS_ERR(trans))
-			return PTR_ERR(trans);
+		trans = btrfs_attach_transaction(fs_info->extent_root);
+		if (IS_ERR(trans)) {
+			if (PTR_ERR(trans) != -ENOENT &&
+			    PTR_ERR(trans) != -EROFS)
+				return PTR_ERR(trans);
+			trans = NULL;
+		}
+	}
+
+	if (trans)
 		btrfs_get_tree_mod_seq(fs_info, &tree_mod_seq_elem);
-	} else {
+	else
 		down_read(&fs_info->commit_root_sem);
-	}
 
 	ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid,
 				   tree_mod_seq_elem.seq, &refs,
@@ -1951,7 +1961,7 @@ int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
 
 	free_leaf_list(refs);
 out:
-	if (!search_commit_root) {
+	if (trans) {
 		btrfs_put_tree_mod_seq(fs_info, &tree_mod_seq_elem);
 		btrfs_end_transaction(trans);
 	} else {