Hi Qu,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on v5.9-rc4]
[also build test ERROR on next-20200908]
[cannot apply to kdave/for-next btrfs/next]
[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/Qu-Wenruo/btrfs-add-read-only-support-for-subpage-sector-size/20200908-155601
base:    f4d51dffc6c01a9e94650d95ce0104964f8ae822
config: i386-randconfig-a016-20200908 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
reproduce (this is a W=1 build):
        # save the attached .config to linux build tree
        make W=1 ARCH=i386 

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 >>):

   ld: fs/btrfs/extent_io.o: in function `release_extent_buffer':
>> fs/btrfs/extent_io.c:5361: undefined reference to `__udivdi3'
   ld: fs/btrfs/extent_io.o: in function `find_extent_buffer':
   fs/btrfs/extent_io.c:5145: undefined reference to `__udivdi3'
   ld: fs/btrfs/extent_io.o: in function `alloc_extent_buffer':
   fs/btrfs/extent_io.c:5305: undefined reference to `__udivdi3'

# https://github.com/0day-ci/linux/commit/d31cf6896006df8bbb0adfd39919bfb7926ded08
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Qu-Wenruo/btrfs-add-read-only-support-for-subpage-sector-size/20200908-155601
git checkout d31cf6896006df8bbb0adfd39919bfb7926ded08
vim +5361 fs/btrfs/extent_io.c

  5346	
  5347	static int release_extent_buffer(struct extent_buffer *eb)
  5348		__releases(&eb->refs_lock)
  5349	{
  5350		lockdep_assert_held(&eb->refs_lock);
  5351	
  5352		WARN_ON(atomic_read(&eb->refs) == 0);
  5353		if (atomic_dec_and_test(&eb->refs)) {
  5354			if (test_and_clear_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags)) {
  5355				struct btrfs_fs_info *fs_info = eb->fs_info;
  5356	
  5357				spin_unlock(&eb->refs_lock);
  5358	
  5359				spin_lock(&fs_info->buffer_lock);
  5360				radix_tree_delete(&fs_info->buffer_radix,
> 5361						  eb->start / fs_info->sectorsize);
  5362				spin_unlock(&fs_info->buffer_lock);
  5363			} else {
  5364				spin_unlock(&eb->refs_lock);
  5365			}
  5366	
  5367			btrfs_leak_debug_del(&eb->fs_info->eb_leak_lock, &eb->leak_list);
  5368			/* Should be safe to release our pages at this point */
  5369			btrfs_release_extent_buffer_pages(eb);
  5370	#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
  5371			if (unlikely(test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags))) {
  5372				__free_extent_buffer(eb);
  5373				return 1;
  5374			}
  5375	#endif
  5376			call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
  5377			return 1;
  5378		}
  5379		spin_unlock(&eb->refs_lock);
  5380	
  5381		return 0;
  5382	}
  5383	

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