reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git/commit/?id=fcdc00137b51b2bfb81523f82122c1c8269c4c65
        git remote add frederic-dynticks https://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
        git fetch --no-tags frederic-dynticks kthread/core-v5
        git checkout fcdc00137b51b2bfb81523f82122c1c8269c4c65
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs