reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/sashal/linux.git/commit/?id=56df6f6c1c97a778da82fad64b7e60be5cce2a9d
        git remote add sashal https://git.kernel.org/pub/scm/linux/kernel/git/sashal/linux.git
        git fetch --no-tags sashal spec
        git checkout 56df6f6c1c97a778da82fad64b7e60be5cce2a9d
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs