snap refresh of core and other snaps fails

[Ondrej Kubik]

snap version
snap 2.44.2+git1700.0aba8dd~ubuntu16.04.1
snapd 2.44.2+git1700.0aba8dd~ubuntu16.04.1
series 16
ubuntu 18.04
kernel 4.15.0-88-generic

More info about failed change and snap causing it
https://paste.ubuntu.com/p/n9kvmtMDgp/

[Ondrej Kubik (ondrak)]

snap remove also fails:
snap remove dragonboard-builder
error: cannot perform the following tasks:
- Disconnect dragonboard-builder:ssh-public-keys from core:ssh-public-keys (cannot update mount namespace of snap "dragonboard-builder": cannot update preserved namespace of snap "dragonboard-builder": cannot update snap namespace: no such file or directory)

snap disconnect dragonboard-builder:home
error: cannot perform the following tasks:
- Disconnect dragonboard-builder:home from core:home (cannot update mount namespace of snap "dragonboard-builder": cannot update preserved namespace of snap "dragonboard-builder": cannot update snap namespace: no such file or directory)

[Zygmunt Krynicki (zyga)]

In case the pastebin goes away, the principal factor is:

base: core18
confinement: strict
layout:
  /etc/mke2fs.conf:
    bind-file: $SNAP_COMMON/etc/mke2fs.conf
  /etc/mtools.conf:
    bind-file: $SNAP_COMMON/etc/mtools.conf

[Zygmunt Krynicki (zyga)]

I cannot reproduce the issue with the following snap (attached).

Ondra, can you check if the test snap reproduces the issue on your system?

[Zygmunt Krynicki (zyga)]

I've attempted to expand the reproducer but failed to see any problems:

I've pushed my code as https://github.com/zyga/snapd/commit/fd7033d86c0237ee887084554205f20a1014d3cc