This fix went into 4.10 and looks like it is needed for the 4.9-stable branch:
commit d47b8715953ad0cf82bb0a9d30d7b11d83bc9c11 Author: Chao Yu yuchao0@huawei.com Date: Sat Nov 5 11:12:40 2016 +0800
Revert "f2fs: do not recover from previous remained wrong dnodes"
Ben.