Hi Michal,

[auto build test ERROR on v4.5-rc6]
[also build test ERROR on next-20160229]
[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/mm-fork-make-dup_mmap-wait-for-mmap_sem-for-write-killable/20160301-021107
config: x86_64-lkp (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   kernel/fork.c: In function 'dup_mmap':
>> kernel/fork.c:405:2: 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 +405 kernel/fork.c

   399		struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
   400		struct rb_node **rb_link, *rb_parent;
   401		int retval;
   402		unsigned long charge;
   403	
   404		uprobe_start_dup_mmap();
 > 405		if (down_write_killable(&oldmm->mmap_sem)) {
   406			retval = -EINTR;
   407			goto fail_uprobe_end;
   408		}

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