Re: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD

[Christian Brauner <brauner@kernel.org>]

On Sat, May 20, 2023 at 10:11:36PM +0800, kernel test robot wrote:
> Hi Alexander,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on net-next/main]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
> base:   net-next/main
> patch link:    https://lore.kernel.org/r/20230517113351.308771-2-aleksandr.mikhalitsyn%40canonical.com
> patch subject: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD
> config: powerpc-randconfig-s043-20230517
> compiler: powerpc-linux-gcc (GCC) 12.1.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # apt-get install sparse
>         # sparse version: v0.6.4-39-gce1a6720-dirty
>         # https://github.com/intel-lab-lkp/linux/commit/969a57c99c9d50bfebd0908f5157870b36c271c7
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
>         git checkout 969a57c99c9d50bfebd0908f5157870b36c271c7
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc olddefconfig
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202305202107.BQoPnLYP-lkp@intel.com/
> 
> All errors (new ones prefixed by >>, old ones prefixed by <<):
> 
> >> ERROR: modpost: "pidfd_prepare" [net/unix/unix.ko] undefined!

TLI, that AF_UNIX can be a kernel module...
I'm really not excited in exposing pidfd_prepare() to non-core kernel
code. Would it be possible to please simply refuse SO_PEERPIDFD and
SCM_PIDFD if AF_UNIX is compiled as a module? I feel that this must be
super rare because it risks breaking even simplistic userspace.