reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git/commit/?id=dadb85bad8e5007cbd0e52309e3a8d8e2d125544
        git remote add viro-vfs https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git
        git fetch --no-tags viro-vfs work.debugfs
        git checkout dadb85bad8e5007cbd0e52309e3a8d8e2d125544
        # 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 SHELL=/bin/bash block/