[Bug 1891224] Re: [Hyper-V] VSS and File Copy daemons intermittently fails to start

[Marcelo Cerri]

Changes submitted to our SRU cycle for groovy, focal, bionic and xenial.

Cover letter: https://lists.ubuntu.com/archives/kernel-
team/2020-August/112922.html

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Title:
   [Hyper-V] VSS and File Copy daemons intermittently fails to start

Status in linux package in Ubuntu:
  In Progress
Status in systemd package in Ubuntu:
  Invalid
Status in linux source package in Xenial:
  In Progress
Status in systemd source package in Xenial:
  Invalid
Status in linux source package in Bionic:
  In Progress
Status in systemd source package in Bionic:
  Invalid
Status in linux source package in Focal:
  In Progress
Status in systemd source package in Focal:
  Invalid
Status in linux source package in Groovy:
  In Progress
Status in systemd source package in Groovy:
  Invalid

Bug description:
  [Impact]

  We have most reliably reproduced this on a Standard_B1s in Azure in
  the North Europe region (>80% of the time). Tests in other regions/VM
  types do not show this failure as often (<1%). We have reproduced this
  in Xenial, Bionic, Focal, and Groovy. We saw an increase of test
  failures around a month ago.

  From the journal :

  Aug 11 09:55:28 ubuntu systemd[1]: sys-devices-virtual-misc-vmbus\x21hv_vss.device: Job sys-devices-virtual-misc-vmbus\x21hv_vss.device/start tim>
  Aug 11 09:55:28 ubuntu systemd[1]: Timed out waiting for device sys-devices-virtual-misc-vmbus\x21hv_vss.device.
  Aug 11 09:55:28 ubuntu systemd[1]: Dependency failed for Hyper-V VSS Protocol Daemon.
  Aug 11 09:55:28 ubuntu systemd[1]: hv-vss-daemon.service: Job hv-vss-daemon.service/start failed with result 'dependency'.
  Aug 11 09:55:28 ubuntu systemd[1]: sys-devices-virtual-misc-vmbus\x21hv_vss.device: Job sys-devices-virtual-misc-vmbus\x21hv_vss.device/start fai>
  Aug 11 09:55:28 ubuntu systemd[1]: sys-devices-virtual-misc-vmbus\x21hv_fcopy.device: Job sys-devices-virtual-misc-vmbus\x21hv_fcopy.device/start>
  Aug 11 09:55:28 ubuntu systemd[1]: Timed out waiting for device sys-devices-virtual-misc-vmbus\x21hv_fcopy.device.
  Aug 11 09:55:28 ubuntu systemd[1]: Dependency failed for Hyper-V File Copy Protocol Daemon.

  We've seen problems in the past with KVP daemons that looked very
  similar : https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1820063

  
  [Test Case]

  There two main scenarios that need to be tested:

  1. Azure instances:

     - Just start an azure instance using our Ubuntu images and check
  the the status of the hv-vss-daemon and hv-fcopy-daemon services using
  systemctl.

     - If the issue is solved they shouldn't be listed as failed.

  2. Local Hyper-V VM:

     - Create a local Hyper-V instance and enable the two systemd
  services if necessary (hv-vss-daemon and hv-fcopy-daemon) and reboot.

     - You can change the integration services that are enable to the
  guest.

       1. With desktop integration and the backup feature disabled, the hv-fcopy-daemon and the hv-vss-daemon service, respectively should not be listed as failed.
       2. With the same features enabled the services should start without errors.

  
  [Regression Potential] 

  The major risk with a potential regression is that those systemd
  service units are shipped by a package produced by our generic kernels
  and not the linux-azure kernel. So in case of a regression we might
  need to re-spin the generic kernels.

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