With Kernel Version 4.12.14-lp151.28.10-default it's not possible to mount a
ext4 disk with Mandatory Locking enabled. After boot, the filesystem is mounted
read-only and without the 'mand' option. In this case this was the root
filesystem!

Kernel 4.4.162-78-default works like it should!

If you try to manual mount another ext4 disk, you get a simple 'Access denied'
message. 

mount /dev/xvdd1 -o mand /test
mount: /test: Zugriff verweigert.

Manual mount with the '4.4.162-78-default works'.

Unfortunately there is no more logging information to find.

We use Xen 4.12.0_12-lp151.1 on SuSE 15.1 as host and and the domU with the
problem is a 'pv' SuSE 15.1.

# /etc/fstab
/dev/xvda1      /       ext4    acl,mand,user_xattr 1 1

The domU was running 42.3 with these settings before. After the upgrade to 15.1
AND with kernel 4.12.14-lp151.28.10-default it doesn't work anymore.