Re: [PATCH net-next] net: fix recent csum changes

On Fri, Dec 3, 2021 at 7:34 PM kernel test robot [off-list ref] wrote:

Hi Eric,

I love your patch! Perhaps something to improve:

[auto build test WARNING on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Eric-Dumazet/net-fix-recent-csum-changes/20211204-025401
base:   https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git 43332cf97425a3e5508c827c82201ecc5ddd54e0
config: parisc-randconfig-s031-20211203 (https://download.01.org/0day-ci/archive/20211204/202112041104.gPgP3Z6U-lkp@intel.com/config)
compiler: hppa64-linux-gcc (GCC) 11.2.0
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-dirty
        # https://github.com/0day-ci/linux/commit/c13fbd113358fb59f76f76d25a1fdb57379c4b9c
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Eric-Dumazet/net-fix-recent-csum-changes/20211204-025401
        git checkout c13fbd113358fb59f76f76d25a1fdb57379c4b9c
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=parisc SHELL=/bin/bash net/core/ net/ipv4/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>

Yes, keeping sparse happy with these checksum is not easy.

I will add and use this helper, unless someone has a better idea.

diff --git a/include/net/checksum.h b/include/net/checksum.h
index 5b96d5bd6e54532a7a82511ff5d7d4c6f18982d5..5218041e5c8f93cd369a2a3a46add3e6a5e41af7

100644

--- a/include/net/checksum.h
+++ b/include/net/checksum.h

@@ -180,4 +180,8 @@ static inline void remcsum_unadjust(__sum16 *psum,

__wsum delta)
        *psum = csum_fold(csum_sub(delta, (__force __wsum)*psum));
 }

+static inline __wsum wsum_negate(__wsum val)
+{
+       return (__force __wsum)-((__force u32)val);
+}
 #endif