[Bug 1994002] Re: [SRU] migration was active, but no RAM info was set

[Mauricio Faria de Oliveira]

Thanks, Brett!

Very minor nitpicks left (changelog entry/release for lunar,
and URL for Origin:), I can handle those.

For Lunar/devel release, I'll send a MR for Christian to
review/upload (my upload rights are for stable releases).

This includes a fix to FTBFS per a package change in the
last 24 hours :) happy to catch it now!

It's currently (re)build-testing on all supported archs.
If all goes well now, I'll send the MR for Lunar, and
once it lands, we'll proceed w/ SRUs.

...

I also played with GDB for a synthetic reproducer.
It seems to be possible, but needs a little more study
on the monitor path.  We can sync on that later!

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Title:
  [SRU] migration was active, but no RAM info was set

Status in Ubuntu Cloud Archive:
  New
Status in Ubuntu Cloud Archive ussuri series:
  New
Status in qemu package in Ubuntu:
  In Progress
Status in qemu source package in Bionic:
  In Progress
Status in qemu source package in Focal:
  In Progress
Status in qemu source package in Jammy:
  In Progress
Status in qemu source package in Kinetic:
  In Progress

Bug description:
  [Impact]

   * While live-migrating many instances concurrently, libvirt sometimes
  return `internal error: migration was active, but no RAM info was
  set:`

   * Effects of this bug are mostly observed in large scale clusters
  with a lot of live migration activity.

   * Has second order effects for consumers of migration monitor such as
  libvirt and openstack.

  [Test Case]
  Steps to Reproduce:
  1. live evacuate a compute
  2. live migration of one or more instances fails with the above error

  N.B Due to the nature of this bug it is difficult consistently reproduce.
  In an environment where it has been observed it is estimated to occur approximately 1/1000 migrations.

  [Where problems could occur]
   * In the event of a regression the migration monitor may report an inconsistent state.

  [Original Bug Description]

  While live-migrating many instances concurrently, libvirt sometimes return internal error: migration was active, but no RAM info was set:
  ~~~
  2022-03-30 06:08:37.197 7 WARNING nova.virt.libvirt.driver [req-5c3296cf-88ee-4af6-ae6a-ddba99935e23 - - - - -] [instance: af339c99-1182-4489-b15c-21e52f50f724] Error monitoring migration: internal error: migration was active, but no RAM info was set: libvirt.libvirtError: internal error: migration was active, but no RAM info was set
  ~~~

  From upstream bug: https://bugzilla.redhat.com/show_bug.cgi?id=2074205

  [Other Information]
  Related bug: https://bugs.launchpad.net/nova/+bug/1982284

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