Hi Dmitry,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[cannot apply to v5.4-rc2 next-20191010]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Dmitry-Safonov/kernel-Introduce-Time-Namespace/20191014-075119
config: parisc-b180_defconfig (attached as .config)
compiler: hppa-linux-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=parisc 

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

All errors (new ones prefixed by >>):

   kernel/time/namespace.o: In function `timens_set_vvar_page.isra.8.part.9':
   (.text+0x130): undefined reference to `arch_get_vdso_data'
   kernel/time/namespace.o: In function `timens_install':
>> (.text+0x6e0): undefined reference to `vdso_join_timens'
   kernel/time/namespace.o: In function `timens_on_fork':
   (.text+0x804): undefined reference to `vdso_join_timens'

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