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

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 ?

 # echo 'module overlay +mp' > /sys/kernel/debug/dynamic_debug/control
 # strace -o /tmp/strace mv foo bar
 # dmesg | grep overlay > /tmp/debug

And post the /tmp/strace and /tmp/debug files.

Hello,

Quoted 4 lines

 # echo 'module overlay +mp' > /sys/kernel/debug/dynamic_debug/control
 # strace -o /tmp/strace mv foo bar
 # dmesg | grep overlay > /tmp/debug

Quoted 1 line

And post the /tmp/strace and /tmp/debug files.

# strace -o /tmp/strace mv OVERLAYFS foo
mv: cannot move ‘OVERLAYFS’ to a subdirectory of itself, ‘foo’

files attached...

Do you have

CONFIG_EXT4_USE_FOR_EXT2=y

in your kernel's .config? If not, then you should.

You'll also need

a4859d75944a ("ovl: fix dentry leak for default_permissions")

from the overlayfs-linus branch of

git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git

otherwise "default_permissions" will misbehave.