1 files changed, 34 insertions, 17 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 0531cb9a3ba9..d826fbaf7d50 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -718,7 +718,7 @@ out:
  * read tree blocks and add keys where required.
  */
 static int add_missing_keys(struct btrfs_fs_info *fs_info,
-			    struct preftrees *preftrees)
+			    struct preftrees *preftrees, bool lock)
 {
 	struct prelim_ref *ref;
 	struct extent_buffer *eb;
@@ -742,12 +742,14 @@ static int add_missing_keys(struct btrfs_fs_info *fs_info,
 			free_extent_buffer(eb);
 			return -EIO;
 		}
-		btrfs_tree_read_lock(eb);
+		if (lock)
+			btrfs_tree_read_lock(eb);
 		if (btrfs_header_level(eb) == 0)
 			btrfs_item_key_to_cpu(eb, &ref->key_for_search, 0);
 		else
 			btrfs_node_key_to_cpu(eb, &ref->key_for_search, 0);
-		btrfs_tree_read_unlock(eb);
+		if (lock)
+			btrfs_tree_read_unlock(eb);
 		free_extent_buffer(eb);
 		prelim_ref_insert(fs_info, &preftrees->indirect, ref, NULL);
 		cond_resched();
@@ -1228,7 +1230,7 @@ again:
 
 	btrfs_release_path(path);
 
-	ret = add_missing_keys(fs_info, &preftrees);
+	ret = add_missing_keys(fs_info, &preftrees, path->skip_locking == 0);
 	if (ret)
 		goto out;
 
@@ -1290,9 +1292,14 @@ again:
 				}
 				btrfs_tree_read_lock(eb);
 				btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
+				if (!path->skip_locking) {
+					btrfs_tree_read_lock(eb);
+					btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
+				}
 				ret = find_extent_in_eb(eb, bytenr,
 							*extent_item_pos, &eie);
-				btrfs_tree_read_unlock_blocking(eb);
+				if (!path->skip_locking)
+					btrfs_tree_read_unlock_blocking(eb);
 				free_extent_buffer(eb);
 				if (ret < 0)
 					goto out;
@@ -1452,8 +1459,8 @@ 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.
  */
@@ -1476,13 +1483,16 @@ 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 {
@@ -1515,6 +1525,7 @@ 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;
@@ -1903,13 +1914,19 @@ 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,
@@ -1941,7 +1958,7 @@ 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 {