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[Luis Henriques <luis.henriques@xxxxxxxxxxxxx>]

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Xenial)
       Status: New => Fix Committed

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https://bugs.launchpad.net/bugs/1647400

Title:
  system freeze when swapping to encrypted swap partition

Status in Ubuntu on IBM z Systems:
  In Progress
Status in linux package in Ubuntu:
  In Progress
Status in linux source package in Xenial:
  Fix Committed

Bug description:
  == Comment: #0 - Bernd-Rainer Bresser <BRESSERB@xxxxxxxxxx> - 2016-12-05 04:27:00 ==
  +++ This bug was initially created as a clone of Bug #147836 +++

  ---Problem Description---
  When the system is installed with encrypted swap partition the attempt to swap ends in a system freeze. No error, no dump, the system needs to be reloaded.
   
  Contact Information = Bernd-Rainer Bresser/Germany/IBM, Wen Yi AG Gao/China/IBM 
   
  ---uname output---
  Linux s38lp65 4.4.0-36-generic #55-Ubuntu SMP Thu Aug 11 18:05:09 UTC 2016 s390x s390x s390x GNU/Linux
   
  Machine Type = z13 LPAR 
   
  ---System Hang---
   System is frozen. No error, no dump, the system needs to be reloaded.
   
  ---Debugger---
  A debugger is not configured
   
  ---Steps to Reproduce---
   1. install a system with encrypted swap partition. This can be done using the installer or via manual updates to /etc/fstab and /etc/crypttab.

  2. Verify encrypted swap partition exists
   cryptsetup status kvmibm-swap
  /dev/mapper/kvmibm-swap is active and is in use.
    type:    PLAIN
    cipher:  aes-xts-plain64:sha256
    keysize: 256 bits
    device:  /dev/dasda2
    offset:  0 sectors
    size:    8388672 sectors
    mode:    read/write

  3. force swapping
  this can be done by a command like this (if the system has 8GB memory)
  dd if=/dev/zero of=/dev/null ibs=16k obs=8G count=2MB
   
  Stack trace output:
   no
   
  Oops output:
   no
   
  System Dump Location:
   
   
  *Additional Instructions for Bernd-Rainer Bresser/Germany/IBM, Wen Yi AG Gao/China/IBM: 
  -Attach sysctl -a output output to the bug.

  == Comment: #1 - Bernd-Rainer Bresser <BRESSERB@xxxxxxxxxx> - 2016-12-05 04:33:24 ==
  - the problem was originally found on KVM for IBM z 1.1.3
  - test on Ubuntu 16.04.1 showed the same issue here
  - on KVM for IBM z 1.1.3 the problem could be solved/circumvented by reverting
         commit 564e81a57f9788b1475127012e0fd44e9049e342
        Author: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
        Date:   Fri Feb 5 15:36:30 2016 -0800
              mm, vmstat: fix wrong WQ sleep when memory reclaim doesn't make any progress

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