reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git/commit/?id=65ca28f0c264b60230a69b605e493aa79faba691
        git remote add boqun https://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git
        git fetch --no-tags boqun rust-atomic-v3
        git checkout 65ca28f0c264b60230a69b605e493aa79faba691
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs