[Bug 1887373] Re: upgrade from 18.04 to 20.04 hangs on lvm2 snapshot

[Denny]

These are the dpkg processes hanging during the upgrade:

me at PROX15:~$ ps aux | grep dpkg
root     21111  0.0  0.0  24868 14308 pts/7    Ss+  12:58   0:00 /usr/bin/dpkg --force-overwrite --status-fd 115 --configure --pending
root     21141  0.0  0.0  31500 21100 pts/7    S+   12:58   0:00 /usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/memtest86+.postinst configure 5.01-3ubuntu2

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https://bugs.launchpad.net/bugs/1887373

Title:
  upgrade from 18.04 to 20.04 hangs on lvm2 snapshot

Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  When trying to upgrade my Kubuntu 18.04 to Kubuntu 20.04 by running

  sudo do-release-upgrade -d

  I get at a point where the installer reads:

  ...
      File descriptor 3 (pipe:[366994]) leaked on vgs invocation. Parent ID 31982: /usr/sbin/grub-probe

  ...
  grub-probe: error: unknown filesystem.
      File descriptor 3 (pipe:[366994]) leaked on vgs invocation. Parent ID 31982: /usr/sbin/grub-probe
  ...

  Found Ubuntu 18.04.4 LTS (18.04) on dev/,apper/kubuntu--vg-snap
  Adding boot menu entry for EFI firmware configuration
  done
  ...

  At this point the installer hangs for at least 35 min. Killing it and
  restarting leads to a kernel panic.

  
  This is on a laptop with lvm2, using an lvm snapshot before the upgrade

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