reproduce (this is a W=1 build):
        git checkout 3a8660878839faadb4f1a6dd72c3179c1df56787
        b4 shazam https://lore.kernel.org/r/20251021-work-namespace-nstree-listns-v1-16-ad44261a8a5b@kernel.org

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 prepare