[mjw1007]

It's very strange that adding/updating documentation isn't treated as a basic requirement for a patch that adds to or modifies Linux's public interfaces.

[milcron]

For the BSDs, incorrect or missing man pages are considered a serious bug.

[dom0]

Man pages aren't even in the kernel tree.

[caf]

From Documentation/process/submit-checklist.rst:

  19) All new userspace interfaces are documented in ``Documentation/ABI/``.
      See ``Documentation/ABI/README`` for more information.
      Patches that change userspace interfaces should be CCed to
      [e-mail].