reproduce:
        git checkout linus/master
        b4 shazam https://lore.kernel.org/r/20240917143402.930114-5-boqun.feng@gmail.com
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs