ext4 filesystem corruption with 4.10-rc2 on ppc64le

Hi,

I'm consistently seeing ext4 filesystem corruption using a mainline
kernel. It doesn't take much to trigger it - download a ppc64le Ubuntu
cloud image, boot it in KVM and run:

sudo apt-get update
sudo apt-get dist-upgrade
sudo reboot

And it never makes it back up, dying with rather severe filesystem
corruption.

I've narrowed it down to:

64e1c57fa474 ("ext4: Use clean_bdev_aliases() instead of iteration")
e64855c6cfaa ("fs: Add helper to clean bdev aliases under a bh and use it")
ce98321bf7d2 ("fs: Remove unmap_underlying_metadata")

Backing these patches out fixes the issue.

Anton