Commit fd7732e0 ("fs/locks: create a tree of dependent requests.")
has put blocked locks into a tree.

So, with a for loop, we can't check all locks information.

To solve this problem, we should traverse the tree.
Signed-off-by: Luo Longjun <luolongjun@huawei.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>