1 files changed, 45 insertions, 6 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index ff9f0d41987e..feec49e6f9c8 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5472,23 +5472,62 @@ static int check_ref_exists(struct btrfs_trans_handle *trans,
 			    struct btrfs_root *root, u64 bytenr, u64 parent,
 			    int level)
 {
+	struct btrfs_delayed_ref_root *delayed_refs;
+	struct btrfs_delayed_ref_head *head;
 	struct btrfs_path *path;
 	struct btrfs_extent_inline_ref *iref;
 	int ret;
+	bool exists = false;
 
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
-
+again:
 	ret = lookup_extent_backref(trans, path, &iref, bytenr,
 				    root->fs_info->nodesize, parent,
 				    btrfs_root_id(root), level, 0);
+	if (ret != -ENOENT) {
+		/*
+		 * If we get 0 then we found our reference, return 1, else
+		 * return the error if it's not -ENOENT;
+		 */
+		btrfs_free_path(path);
+		return (ret < 0 ) ? ret : 1;
+	}
+
+	/*
+	 * We could have a delayed ref with this reference, so look it up while
+	 * we're holding the path open to make sure we don't race with the
+	 * delayed ref running.
+	 */
+	delayed_refs = &trans->transaction->delayed_refs;
+	spin_lock(&delayed_refs->lock);
+	head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
+	if (!head)
+		goto out;
+	if (!mutex_trylock(&head->mutex)) {
+		/*
+		 * We're contended, means that the delayed ref is running, get a
+		 * reference and wait for the ref head to be complete and then
+		 * try again.
+		 */
+		refcount_inc(&head->refs);
+		spin_unlock(&delayed_refs->lock);
+
+		btrfs_release_path(path);
+
+		mutex_lock(&head->mutex);
+		mutex_unlock(&head->mutex);
+		btrfs_put_delayed_ref_head(head);
+		goto again;
+	}
+
+	exists = btrfs_find_delayed_tree_ref(head, root->root_key.objectid, parent);
+	mutex_unlock(&head->mutex);
+out:
+	spin_unlock(&delayed_refs->lock);
 	btrfs_free_path(path);
-	if (ret == -ENOENT)
-		return 0;
-	if (ret < 0)
-		return ret;
-	return 1;
+	return exists ? 1 : 0;
 }
 
 /*