Yeah, this issue has mostly been seen on ZFS, likely because we have far more ZFS users than LVM.
Our best guess is that it has to do with a system having running containers, combined with an update to some of the core snaps and combined with a LXD snap update, some combination of this then results in a mount namespace configuration which our reshuffling tool can’t deal with, resulting in the error we can see in your journal.
Unfortunately fixing this properly will require us being able to reproduce this issue at will so we can significantly increase the debugging in the reshuffling tool as well as take detailed dumps of all mount tables at play.
In your case, a workaround for that one system would likely be:
- nsenter -t 1471 -m umount -l /var/snap/lxd/common/shmounts
- nsenter -t 1471 -m umount -l /var/snap/lxd/common/shmounts
- nsenter -t 1471 -m umount -l /var/snap/lxd/common/shmounts/storage-pools/primary/containers/lxc14fc3901
That would undo the two level of overmounting and then unmount the hidden mount.