+ * A transaction used for relocating a block group was committed or is about to
+ * finish its commit. Release our paths and restart the search, so that we are
+ * not using stale extent buffers:
+ *
+ * 1) For levels > 0, we are only holding references of extent buffers, without
+ * any locks on them, which does not prevent them from having been relocated
+ * and reallocated after the last time we released the commit root semaphore.
+ * The exception are the root nodes, for which we always have a clone, see
+ * the comment at btrfs_compare_trees();
+ *
+ * 2) For leaves, level 0, we are holding copies (clones) of extent buffers, so
+ * we are safe from the concurrent relocation and reallocation. However they
+ * can have file extent items with a pre relocation disk_bytenr value, so we
+ * restart the start from the current commit roots and clone the new leaves so
+ * that we get the post relocation disk_bytenr values. Not doing so, could
+ * make us clone the wrong data in case there are new extents using the old
+ * disk_bytenr that happen to be shared.
+ */
+static int restart_after_relocation(struct btrfs_path *left_path,
+ struct btrfs_path *right_path,
+ const struct btrfs_key *left_key,
+ const struct btrfs_key *right_key,
+ int left_level,
+ int right_level,
+ const struct send_ctx *sctx)
+{
+ int root_level;
+ int ret;
+
+ lockdep_assert_held_read(&sctx->send_root->fs_info->commit_root_sem);
+
+ btrfs_release_path(left_path);
+ btrfs_release_path(right_path);
+
+ /*
+ * Since keys can not be added or removed to/from our roots because they
+ * are readonly and we do not allow deduplication to run in parallel
+ * (which can add, remove or change keys), the layout of the trees should
+ * not change.
+ */
+ left_path->lowest_level = left_level;
+ ret = search_key_again(sctx, sctx->send_root, left_path, left_key);
+ if (ret < 0)
+ return ret;
+
+ right_path->lowest_level = right_level;
+ ret = search_key_again(sctx, sctx->parent_root, right_path, right_key);
+ if (ret < 0)
+ return ret;
+
+ /*
+ * If the lowest level nodes are leaves, clone them so that they can be
+ * safely used by changed_cb() while not under the protection of the
+ * commit root semaphore, even if relocation and reallocation happens in
+ * parallel.
+ */
+ if (left_level == 0) {
+ ret = replace_node_with_clone(left_path, 0);
+ if (ret < 0)
+ return ret;
+ }
+
+ if (right_level == 0) {
+ ret = replace_node_with_clone(right_path, 0);
+ if (ret < 0)
+ return ret;
+ }
+
+ /*
+ * Now clone the root nodes (unless they happen to be the leaves we have
+ * already cloned). This is to protect against concurrent snapshotting of
+ * the send and parent roots (see the comment at btrfs_compare_trees()).
+ */
+ root_level = btrfs_header_level(sctx->send_root->commit_root);
+ if (root_level > 0) {
+ ret = replace_node_with_clone(left_path, root_level);
+ if (ret < 0)
+ return ret;
+ }
+
+ root_level = btrfs_header_level(sctx->parent_root->commit_root);
+ if (root_level > 0) {
+ ret = replace_node_with_clone(right_path, root_level);
+ if (ret < 0)
+ return ret;
+ }
+
+ return 0;
+}
+
+/*