is mounting subvolumes with a read-only root subvolume allowed?

["Zbigniew Jędrzejewski-Szmek" <zbyszek@in.waw.pl>]

Hi,
I have a box with / and /home being subvolumes from the same btrfs filesystem.

/etc/fstab:
UUID=c0686...      /      btrfs subvol=root,x-systemd.device-timeout=0 1 1
UUID=c0686...      /home  btrfs subvol=home,x-systemd.device-timeout=0 1 1
...

/ is initially mounted readonly by the initramfs, and then after switching
to the real system, /home is attempted to be mounted in parallel with /
being remounted rw. If remounting rw happens first, boot proceeds. If
mounting /home is attempted to realy, it fails.

$ /bin/mount /home
mount: /dev/mapper/luks-765... is already mounted or /home busy
       /dev/mapper/luks-765... is already mounted on /
$ /bin/mount -o remount,rw /
$ /bin/mount /home
$

So, is this expected that the other subvolume must be mounted rw?

Zbyszek