Hi Peter,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on arm64/for-next/core]
[also build test ERROR on linux/master linus/master v5.12-rc1 next-20210304]
[cannot apply to hnaz-linux-mm/master]
[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/Peter-Xu/hugetlb-Disable-huge-pmd-unshare-for-uffd-wp/20210219-071334
base:   https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core
config: mips-randconfig-m031-20210304 (attached as .config)
compiler: mipsel-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/7ede06d6f63e59db4b9dee54f78eeac0c9ca17e4
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Peter-Xu/hugetlb-Disable-huge-pmd-unshare-for-uffd-wp/20210219-071334
        git checkout 7ede06d6f63e59db4b9dee54f78eeac0c9ca17e4
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=mips 

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

All errors (new ones prefixed by >>):

>> mm/hugetlb.c:5376:8: error: conflicting types for 'huge_pmd_share'
    5376 | pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct vma,
         |        ^~~~~~~~~~~~~~
   In file included from mm/hugetlb.c:39:
   include/linux/hugetlb.h:155:8: note: previous declaration of 'huge_pmd_share' was here
     155 | pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
         |        ^~~~~~~~~~~~~~


vim +/huge_pmd_share +5376 mm/hugetlb.c

  5343	
  5344	/*
  5345	 * unmap huge page backed by shared pte.
  5346	 *
  5347	 * Hugetlb pte page is ref counted at the time of mapping.  If pte is shared
  5348	 * indicated by page_count > 1, unmap is achieved by clearing pud and
  5349	 * decrementing the ref count. If count == 1, the pte page is not shared.
  5350	 *
  5351	 * Called with page table lock held and i_mmap_rwsem held in write mode.
  5352	 *
  5353	 * returns: 1 successfully unmapped a shared pte page
  5354	 *	    0 the underlying pte page is not shared, or it is the last user
  5355	 */
  5356	int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
  5357						unsigned long *addr, pte_t *ptep)
  5358	{
  5359		pgd_t *pgd = pgd_offset(mm, *addr);
  5360		p4d_t *p4d = p4d_offset(pgd, *addr);
  5361		pud_t *pud = pud_offset(p4d, *addr);
  5362	
  5363		i_mmap_assert_write_locked(vma->vm_file->f_mapping);
  5364		BUG_ON(page_count(virt_to_page(ptep)) == 0);
  5365		if (page_count(virt_to_page(ptep)) == 1)
  5366			return 0;
  5367	
  5368		pud_clear(pud);
  5369		put_page(virt_to_page(ptep));
  5370		mm_dec_nr_pmds(mm);
  5371		*addr = ALIGN(*addr, HPAGE_SIZE * PTRS_PER_PTE) - HPAGE_SIZE;
  5372		return 1;
  5373	}
  5374	#define want_pmd_share()	(1)
  5375	#else /* !CONFIG_ARCH_WANT_HUGE_PMD_SHARE */
> 5376	pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct vma,
  5377			      unsigned long addr, pud_t *pud)
  5378	{
  5379		return NULL;
  5380	}
  5381	

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