[Bug 1876506] Re: eoan to focal upgrade hangs when lvm snapshot is present

[Julian Andres Klode]

Reset my testing VM to basic eoan, added focal-proposed, and upgraded
memtest86+ to 5.01-3.1ubuntu2.1 from focal-proposed, which worked. For
comparison, yesterday's run against 5.01-3ubuntu1 from the release
pocket did not work.

** Changed in: memtest86+ (Ubuntu Focal)
   Importance: Undecided => Critical

** Changed in: memtest86+ (Ubuntu)
   Importance: Undecided => Critical

** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done verification-done-focal

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Title:
  eoan to focal upgrade hangs when lvm snapshot is present

Status in memtest86+ package in Ubuntu:
  Fix Released
Status in os-prober package in Ubuntu:
  Confirmed
Status in memtest86+ source package in Focal:
  Fix Committed
Status in os-prober source package in Focal:
  Confirmed

Bug description:
  [Impact]
  Upgrading on LVM systems with snapshots hangs

  [Test case]

  - Install VM with eoan, LVM
  - Create snapshot of root
  - Upgrade memtest86+ to focal (download deb and apt install it is enough)

  This hangs, when it shouldn't.

  [Regression potential]
  The change to memtest86+ closes file descriptor 3 when invoking update-grub like other callers do, which fixes the issue. File descriptor 3 is the debconf socket. If update-grub would need to communicate with debconf, it couldn't anymore. But seeing that we do this everywhere else, this should be fine.

  [Original bug report]

  When upgrading from 19.10 (w/ LVM + encypted disks) to 20.04, the
  installer hangs when trying to probe an LVM snapshot volume created
  before the upgrade.

  Steps to reproduce:

  lvcreate -s -L 20G -n preupgrade /dev/vgubuntu/root
  do-release-upgrade -d

  The installer will hang after the following message:

  /usr/sbin/grub-probe: error: unknown filesystem.
  Found Ubuntu 19.10 (19.10) on /dev/mapper/vgubuntu-preupgrade
  done

  Resolution:

  Killing the grub-mount process which is probing the LVM snapshot seems
  to unhang the installer and allow the upgrade to complete without
  issue.

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