Hi Michal,

[auto build test ERROR on next-20160229]
[also build test ERROR on v4.5-rc6]
[cannot apply to drm/drm-next drm-intel/for-linux-next v4.5-rc6 v4.5-rc5 v4.5-rc4]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/Michal-Hocko/change-mmap_sem-taken-for-write-killable/20160229-213258
config: i386-randconfig-x004-201609 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   kernel/fork.c: In function 'dup_mmap':
>> kernel/fork.c:416:6: error: implicit declaration of function 'down_write_killable' [-Werror=implicit-function-declaration]
     if (down_write_killable(&oldmm->mmap_sem)) {
         ^
   cc1: some warnings being treated as errors

vim +/down_write_killable +416 kernel/fork.c

   410		struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
   411		struct rb_node **rb_link, *rb_parent;
   412		int retval;
   413		unsigned long charge;
   414	
   415		uprobe_start_dup_mmap();
 > 416		if (down_write_killable(&oldmm->mmap_sem)) {
   417			uprobe_end_dup_mmap();
   418			return -EINTR;
   419		}

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