** Changed in: linux (Ubuntu)
   Importance: Undecided => High

** Changed in: linux (Ubuntu)
     Assignee: (unassigned) => Canonical Kernel Team (canonical-kernel-team)

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https://bugs.launchpad.net/bugs/1602577

Title:
  [arm64] compute nodes unstable after upgrading from 4.2 to 4.4 kernel

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  Hi,

  In order to investigate bug LP#1531768, we upgraded some arm64 compute
  nodes (swirlices) to a 4.4 kernel. I think it made the VMs work
  better, but the hosts became extremely unstable.

  After some time, getting a shell on them would be impossible.
  Connecting on the VSP, you'd get a prompt, and once you typed your
  username and password, you'd see the motd but the shell would never
  spawn.

  Because of these instability issues, all the arm64 compute nodes are
  now back on 4.2. However, we managed to capture "perf record" data
  when a host was failing. I'll attach it to the bug. Perhaps it will
  give you hints as to what we can do to help you troubleshoot this bug
  further.

  Once we have your instructions, we'll happily reboot one (or a few)
  nodes to 4.4 to continue troubleshooting.

  Thanks !
  --- 
  AlsaDevices:
   total 0
   crw-rw---- 1 root audio 116,  1 Jul 12 12:54 seq
   crw-rw---- 1 root audio 116, 33 Jul 12 12:54 timer
  AplayDevices: Error: [Errno 2] No such file or directory
  ApportVersion: 2.14.1-0ubuntu3.21
  Architecture: arm64
  ArecordDevices: Error: [Errno 2] No such file or directory
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', 
'/dev/snd/timer'] failed with exit code 1:
  CRDA: Error: [Errno 2] No such file or directory
  DistroRelease: Ubuntu 14.04
  Lsusb: Error: command ['lsusb'] failed with exit code 1: unable to initialize 
libusb: -99
  Package: linux (not installed)
  PciMultimedia:
   
  ProcEnviron:
   TERM=screen-256color
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcFB:
   
  ProcKernelCmdLine: console=ttyS0,9600n8r ro compat_uts_machine=armv7l
  ProcVersionSignature: Ubuntu 4.2.0-41.48~14.04.1-generic 4.2.8-ckt11
  RelatedPackageVersions:
   linux-restricted-modules-4.2.0-41-generic N/A
   linux-backports-modules-4.2.0-41-generic  N/A
   linux-firmware                            1.127.22
  RfKill: Error: [Errno 2] No such file or directory
  Tags:  trusty uec-images
  Uname: Linux 4.2.0-41-generic aarch64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups:
   
  _MarkForUpload: True

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