[RPi4] [kernel 5.10] overlayfs

[andiling]

Hello!
I installed the 5.10 kernel package today (linux-raspberrypi4-5.10.10-1-armv7h) and noticed that with the new kernel my overlayfs setup is not working anymore:
The procedure is called through a systemd service unit which I have written by myself. The command is:
$this->bbcode_second_pass_code('', 'mount -t overlay overlay -o lowerdir=/usr/local/vpnserver/base,upperdir=/usr/local/vpnserver/overlay/upper,workdir=/usr/local/vpnserver/overlay/work /usr/local/vpnserver/bin')
It creates the following errors:
$this->bbcode_second_pass_code('', 'Jan 26 16:23:23 raspberry vpnhelper[20787]: mount: /usr/local/vpnserver/bin: overlay konnte nicht im Lese-Schreib-Modus eingehängt werden, (Medium) ist schreibgeschützt..
Jan 26 16:23:23 raspberry kernel: overlayfs: upper fs does not support tmpfile.
Jan 26 16:23:23 raspberry kernel: overlayfs: upper fs does not support tmpfile.')
Funnily enough the command works if I execute it in the shell as root user. However, systemd service should use root as well (I did not specify a certain user).
This happens with 5.10 but not 5.4 and before.
I use a couple of tmpfs but not in the affected directory.
$this->bbcode_second_pass_code('', 'tmpfs 1958452 0 1958452 0% /dev/shm
tmpfs 4096 0 4096 0% /sys/fs/cgroup
tmpfs 1958456 2696 1955760 1% /tmp
tmpfs 1958452 4200 1954252 1% /var/cache
tmpfs 1958452 4 1958448 1% /var/lib/misc
tmpfs 1958452 0 1958452 0% /var/lib/ntp
tmpfs 1958452 7812 1950640 1% /var/lib/pacman/sync
tmpfs 1958452 300 1958152 1% /var/log
tmpfs 1958452 0 1958452 0% /var/spool/mail
tmpfs 1958452 1776 1956676 1% /var/lib/samba
tmpfs 1958452 0 1958452 0% /var/spool/samba
tmpfs 1958452 4 1958448 1% /var/tmp
tmpfs 391688 0 391688 0% /run/user/0')
If succesfully mounted (under 5.4 or manually in shell under 5.10) I have the following mount:
$this->bbcode_second_pass_code('', 'overlay 15187044 2814180 11581860 20% /usr/local/vpnserver/bin')
Does anyone have a clue what may be the issue with the 5.10 kernel regarding my setup?
Thank you so much!
Andreas

[graysky]

If you can mount it outside of systemd, I am not sure what I can do in the kernel package.

[andiling]

Thanks anyways. To circumveit the issue I moved now to unionfs-fuse, sufficient for my purpose and working.