Comment # 21 on bug 1156421 from Fabian Vogt

(In reply to Fabian Vogt from comment #20)
> (In reply to Miroslav Bene�� from comment #18)
> > David, Goldwyn, do you consider the behaviour Fabian described in comment 16
> > as step 3 a bug in the kernel? If not, we should reassign?
> > 
> > Fabian, I assume the issue still exists with the newer kernel. Is that
> > correct?
> 
> I don't know, but I would assume that it's the case too.

Just reproduced the behaviour on 5.6.0 as well:

dd if=/dev/zero of=btrfsfs seek=240 count=0 bs=1M
mkfs.btrfs btrfsfs
mount btrfsfs /mnt
btrfs subvol create /mnt/sv
mount -o remount,ro /mnt
mount -osubvol=/sv btrfsfs /mnt/sv
findmnt # /mnt is RO, /mnt/sv RW
mount -o remount,ro /mnt
findmnt # /mnt is RO, /mnt/sv RO as well
umount /mnt{/sv,}
rm btrfsfs