reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git/commit/?id=107a7f3910694e43dc91f4aa7eb3405158257785
        git remote add viro-vfs https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git
        git fetch --no-tags viro-vfs work.dcache
        git checkout 107a7f3910694e43dc91f4aa7eb3405158257785
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash fs/