1 files changed, 19 insertions, 11 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 3725277f6e08..35cfa388dc0b 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1580,20 +1580,21 @@ int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
 /**
  * btrfs_check_shared - tell us whether an extent is shared
  *
- * @trans: optional trans handle
- *
  * btrfs_check_shared uses the backref walking code but will short
  * circuit as soon as it finds a root or inode that doesn't match the
  * one passed in. This provides a significant performance benefit for
  * 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.
+ *
  * Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
  */
-int btrfs_check_shared(struct btrfs_trans_handle *trans,
-                       struct btrfs_fs_info *fs_info, u64 root_objectid,
-                       u64 inum, u64 bytenr)
+int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr)
 {
+        struct btrfs_fs_info *fs_info = root->fs_info;
+        struct btrfs_trans_handle *trans;
         struct ulist *tmp = NULL;
         struct ulist *roots = NULL;
         struct ulist_iterator uiter;
@@ -1609,14 +1610,18 @@ int btrfs_check_shared(struct btrfs_trans_handle *trans,
                 return -ENOMEM;
         }
 
-        if (trans)
-                btrfs_get_tree_mod_seq(fs_info, &elem);
-        else
+        trans = btrfs_join_transaction(root);
+        if (IS_ERR(trans)) {
+                trans = NULL;
                 down_read(&fs_info->commit_root_sem);
+        } else {
+                btrfs_get_tree_mod_seq(fs_info, &elem);
+        }
+
         ULIST_ITER_INIT(&uiter);
         while (1) {
                 ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
-                                        roots, NULL, root_objectid, inum, 1);
+                                        roots, NULL, root->objectid, inum, 1);
                 if (ret == BACKREF_FOUND_SHARED) {
                         /* this is the only condition under which we return 1 */
                         ret = 1;
@@ -1631,10 +1636,13 @@ int btrfs_check_shared(struct btrfs_trans_handle *trans,
                 bytenr = node->val;
                 cond_resched();
         }
-        if (trans)
+
+        if (trans) {
                 btrfs_put_tree_mod_seq(fs_info, &elem);
-        else
+                btrfs_end_transaction(trans);
+        } else {
                 up_read(&fs_info->commit_root_sem);
+        }
         ulist_free(tmp);
         ulist_free(roots);
         return ret;