Btrfs: don't delete csum for free space cache

index 6d16bea..7c729c3 100644
@@ -605,6 +605,7 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info,
 	head_ref->is_data = is_data;
 	head_ref->ref_root = RB_ROOT;
 	head_ref->processing = 0;
+	head_ref->no_csums = 0;
 
 	spin_lock_init(&head_ref->lock);
 	mutex_init(&head_ref->mutex);

@@ -848,6 +849,13 @@ int btrfs_add_delayed_data_ref(struct btrfs_fs_info *fs_info,
 	head_ref = add_delayed_ref_head(fs_info, trans, &head_ref->node,
 					bytenr, num_bytes, action, 1);
 
+	/*
+	 * If ref_root is the tree root then this is a block group space cache
+	 * extent and doesn't have csums, so we can set no_csums.
+	 */
+	if (ref_root == BTRFS_ROOT_TREE_OBJECTID)
+		head_ref->no_csums = 1;
+
 	add_delayed_data_ref(fs_info, trans, head_ref, &ref->node, bytenr,
 				   num_bytes, parent, ref_root, owner, offset,
 				   action, no_quota);

index a764e23..c464dd3 100644
@@ -101,6 +101,7 @@ struct btrfs_delayed_ref_head {
 	 * the free has happened.
 	 */
 	unsigned int must_insert_reserved:1;
+	unsigned int no_csums:1;
 	unsigned int is_data:1;
 	unsigned int processing:1;
 };

index 74eb29d..23b704e 100644
@@ -2312,7 +2312,7 @@ static int run_one_delayed_ref(struct btrfs_trans_handle *trans,
 		if (insert_reserved) {
 			btrfs_pin_extent(root, node->bytenr,
 					 node->num_bytes, 1);
-			if (head->is_data) {
+			if (head->is_data && !head->no_csums) {
 				ret = btrfs_del_csums(trans, root,
 						      node->bytenr,
 						      node->num_bytes);

@@ -6094,7 +6094,11 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
 		}
 		btrfs_release_path(path);
 
-		if (is_data) {
+		/*
+		 * If the ref root is the tree root then this is a nodatasum
+		 * extent and we can skip the btrfs_del_csums step.
+		 */
+		if (is_data && (root_objectid != BTRFS_ROOT_TREE_OBJECTID)) {
 			ret = btrfs_del_csums(trans, root, bytenr, num_bytes);
 			if (ret) {
 				btrfs_abort_transaction(trans, extent_root, ret);