f2fs: flush dirty meta pages when flushing them

Let's guarantee flusing dirty meta pages to avoid infinite loop.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -1266,6 +1266,9 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
 		if (unlikely(f2fs_cp_error(sbi)))
 			break;
 
+		if (type == F2FS_DIRTY_META)
+			f2fs_sync_meta_pages(sbi, META, LONG_MAX,
+							FS_CP_META_IO);
 		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
 	}
 	finish_wait(&sbi->cp_wait, &wait);