f2fs: fix to don't trigger writeback during recovery

- f2fs_fill_super
 - recover_fsync_data
  - recover_data
   - del_fsync_inode
    - iput
     - iput_final
      - write_inode_now
       - f2fs_write_inode
        - f2fs_balance_fs
         - f2fs_balance_fs_bg
          - sync_dirty_inodes

With data_flush mount option, during recovery, in order to avoid entering
above writeback flow, let's detect recovery status and do skip in
f2fs_balance_fs_bg.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Yunlei He <heyunlei@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -486,6 +486,9 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
 
 void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
 {
+	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
+		return;
+
 	/* try to shrink extent cache when there is no enough memory */
 	if (!available_free_memory(sbi, EXTENT_CACHE))
 		f2fs_shrink_extent_tree(sbi, EXTENT_CACHE_SHRINK_NUMBER);