reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/alexs/linux.git/commit/?id=abf912ed5d786d4c4c66d8ffae229dc099f139c4
        git remote add alexs https://git.kernel.org/pub/scm/linux/kernel/git/alexs/linux.git
        git fetch --no-tags alexs docs-next
        git checkout abf912ed5d786d4c4c66d8ffae229dc099f139c4
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs