NFS/ro: mv: cannot move 'foo' to a subdirectory of itself, 'bar'

["André Roth" <neolynx@gmail.com>]

Hello,

I try to use overlay for network boot clients using an NFS read-only
filesystem. This works pretty well, except renaming files with the mv
command fails:

==========================
# ls -l
-rw-r--r-- 1 root root 785 Mar 27  2016 foo

# mv foo bar
mv: cannot move 'foo' to a subdirectory of itself, 'bar'
==========================

I mount the overlay filesystem as follows in the initrd, where /root is
already mounted read-only from NFS:
==========================
mkdir /writable
mkfs.ext2 /dev/ram0 >/dev/null
mount -n /dev/ram0 /writable >/dev/null

mkdir /writable/upper
mkdir /writable/work

modprobe overlay
mount -t overlay overlay -olowerdir=/root,upperdir=/writable/upper,workdir=/writable/work,default_permissions /root
==========================

kernel version is 4.7.0-rc2, git cloned from
git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git,
using the overlayfs-next branch.

is this a bug ?
can I help anything debugging fixing this ?


Regards,

 André