Hi NeilBrown,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on nfsd/nfsd-next]
[also build test WARNING on kdave/for-next hch-configfs/for-next linus/master v5.14-rc3 next-20210727]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/NeilBrown/expose-btrfs-subvols-in-mount-table-correctly/20210728-064502
base:   git://linux-nfs.org/~bfields/linux.git nfsd-next
config: i386-randconfig-s002-20210728 (attached as .config)
compiler: gcc-10 (Ubuntu 10.3.0-1ubuntu1~20.04) 10.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.3-341-g8af24329-dirty
        # https://github.com/0day-ci/linux/commit/58749022685aea90dfddfb9f8b2fcdc74dee6ec0
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review NeilBrown/expose-btrfs-subvols-in-mount-table-correctly/20210728-064502
        git checkout 58749022685aea90dfddfb9f8b2fcdc74dee6ec0
        # save the attached .config to linux build tree
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 SHELL=/bin/bash fs/btrfs/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)
>> fs/btrfs/inode.c:5868:5: sparse: sparse: symbol 'btrfs_mountpoint_expiry_timeout' was not declared. Should it be static?

Please review and possibly fold the followup patch.

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org