Ansible – Mode 755 for directories and 644 for files recursively

Since version 1.8, Ansible supports symbolic modes. Thus, the following would perform the task you want:

- name: Make my directory tree readable
  file:
    path: dir
    mode: u=rwX,g=rX,o=rX
    recurse: yes

Because X (instead of x) only applies to directories or files with at least one x bit set.