[Bug 1743249] Re: Failed Deployment after timeout trying to retrieve grub cfg

[Steve Langasek]

Regarding grub requesting the same file 4 times, a surprising finding:
I'm able to reproduce this with files of a certain length.  By chance my
grub.cfg was 1 byte shorter than the one maas serves (269 bytes instead
of 270), and I saw multiple requests for this file.

To reproduce this in a VM using UEFI:
- set up dhcp to point to bootx64.efi
- set up tftp with bootx64.efi and grubx64.efi but not grub/grub.cfg
- create files of varying sizes and access them using 'source (pxe)/config-file-on-server'

A simple file consisting of nothing but newlines is sufficient.

confirmed "good" file lengths: 1,2,3,4,266,268,270
confirmed "bad" file lengths: 267,269,271,584,595,627

No pattern established yet.

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https://bugs.launchpad.net/bugs/1743249

Title:
  Failed Deployment after timeout trying to retrieve grub cfg

Status in MAAS:
  Incomplete
Status in grub2 package in Ubuntu:
  New

Bug description:
  A node failed to deploy after it failed to retrieve a grub.cfg from
  MAAS due to a timeout.  In the logs, it's clear that the server tried
  to retrieve the grub cfg many times, over about 30 seconds:

  http://paste.ubuntu.com/26387256/

  We see the same thing for other hosts around the same time:

  http://paste.ubuntu.com/26387262/

  It seems like MAAS is taking way too long to respond to these
  requests.

  This is very similar to bug 1724677, which was happening pre-
  metldown/spectre. The only difference is we don't see "[critical] TFTP
  back-end failed" in the logs anymore.

  I connected to the console on this system and it had errors about
  timing out retrieving the grub-cfg, then it had an error message along
  the lines of "error not an ip" and then "double free".  After I
  connected but before I could get a screenshot the system rebooted and
  was directed by maas to power off, which it did successfully after
  booting to linux.

  Full logs are available here:
  https://10.245.162.101/artifacts/14a34b5a-9321-4d1a-b2fa-
  ed277a020e7c/cpe_cloud_395/infra-logs.tar

  This is with 2.3.0-6434-gd354690-0ubuntu1~16.04.1.

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