Re: [PATCH v2 net 13/17] net: Fix data-races around sysctl_fb_tunnels_only_for_init_net.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   kernel test robot <lkp@intel.com>
Date:   Thu, 18 Aug 2022 16:51:37 +0800
> Hi Kuniyuki,
> 
> Thank you for the patch! Yet something to improve:
> 
> [auto build test ERROR on net/master]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Kuniyuki-Iwashima/net-sysctl-Fix-data-races-around-net-core-XXX/20220818-115941
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git fc4aaf9fb3c99bcb326d52f9d320ed5680bd1cee
> config: riscv-randconfig-r032-20220818 (https://download.01.org/0day-ci/archive/20220818/202208181615.Lu9xjiEv-lkp@intel.com/config)
> compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project aed5e3bea138ce581d682158eb61c27b3cfdd6ec)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install riscv cross compiling tool for clang build
>         # apt-get install binutils-riscv64-linux-gnu
>         # https://github.com/intel-lab-lkp/linux/commit/6bc3dfb3dc4862f4e00ba93c45cd5c0251b85d5b
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Kuniyuki-Iwashima/net-sysctl-Fix-data-races-around-net-core-XXX/20220818-115941
>         git checkout 6bc3dfb3dc4862f4e00ba93c45cd5c0251b85d5b
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All errors (new ones prefixed by >>):
> 
> >> ld.lld: error: undefined symbol: sysctl_fb_tunnels_only_for_init_net
>    >>> referenced by ip_tunnel.c
>    >>>               ipv4/ip_tunnel.o:(ip_tunnel_init_net) in archive net/built-in.a
>    >>> referenced by ip_tunnel.c
>    >>>               ipv4/ip_tunnel.o:(ip_tunnel_init_net) in archive net/built-in.a

Hmm... I tested allmodconfig with x86_64 but it seems not enough...

I don't think just using READ_ONCE() causes regression.
Is this really regression or always-broken stuff in some arch,
or ... clang 16?

Anyway, I'll take a look.