btrfs_try_tree_read_lock
if (!btrfs_try_tree_read_lock(b)) {
ret = btrfs_try_tree_read_lock(next);
if (!btrfs_try_tree_read_lock(next)) {
if (!btrfs_try_tree_read_lock(eb)) {
bool btrfs_try_tree_read_lock(struct extent_buffer *eb);
DEFINE_BTRFS_LOCK_EVENT(btrfs_try_tree_read_lock);