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[Launchpad Bug Tracker <1828596@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package makedumpfile - 1:1.6.5-1ubuntu2

---------------
makedumpfile (1:1.6.5-1ubuntu2) eoan; urgency=medium

  [ Thadeu Lima de Souza Cascardo ]
  * Use maxcpus instead of nr_cpus on ppc64el. (LP: #1828597)
  * Reload kdump when CPU is brought online. (LP: #1828596)

 -- Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>  Fri, 14 Jun
2019 10:58:40 -0300

** Changed in: makedumpfile (Ubuntu Eoan)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1828596

Title:
  kdump fails when crash is triggered after DLPAR cpu add operation

Status in The Ubuntu-power-systems project:
  Confirmed
Status in kexec-tools package in Ubuntu:
  Invalid
Status in makedumpfile package in Ubuntu:
  Fix Released
Status in kexec-tools source package in Xenial:
  New
Status in makedumpfile source package in Xenial:
  New
Status in kexec-tools source package in Bionic:
  New
Status in makedumpfile source package in Bionic:
  New
Status in kexec-tools source package in Cosmic:
  New
Status in makedumpfile source package in Cosmic:
  New
Status in kexec-tools source package in Disco:
  New
Status in makedumpfile source package in Disco:
  New
Status in kexec-tools source package in Eoan:
  Invalid
Status in makedumpfile source package in Eoan:
  Fix Released

Bug description:
  == Comment: #0 - Hari Krishna Bathini - 2019-05-10 05:55:40 ==
  ---Problem Description---
  kdump fails when crash is triggered after CPU add operation.
   
  Machine Type = na 
   
  ---System Hang---
   Crashed in early boot process of kdump kernel after crash

  Had to issue system reset from HMC to reclaim
   
  ---Steps to Reproduce---
   1. Configure kdump.
  2. Add cpu from HMC.
  3. Trigger crash.
  4. Machine hangs after crash as below:

  ---
  [169250.213166] IPI complete
  [169250.234331] kexec: Starting switchover sequence.
  I'm in purgatory
                               --- STRUCK HERE ---
   
  ---uname output---
  na
   
  ---Debugger---
  A debugger is not configured

  == Comment: #1 - Hari Krishna Bathini  - 2019-05-10 05:56:46 ==
  The problem is, kexec udev rule to restart kdump-tools service - when a core is added,
  is not being triggered. The old DT created by kexec (before the core is added)
  is being used by KDump Kernel. So, when system crashes on a thread from
  the added core(s), KDump kernel is failing to get the 'boot_cpuid' and
  eventually failing to boot..

  == Comment: #2 - Hari Krishna Bathini - 2019-05-10 06:02:27 ==
  The udev rule when CPU is added is not triggered because ppc64 does not
  eject add/remove event when a CPU is hot added/removed. It only ejects
  online/offline event to user space when CPU is hot added/removed.

  So, the below udev rules are never triggered when needed:

  SUBSYSTEM=="cpu", ACTION=="add", PROGRAM="/bin/systemctl try-restart kdump-tools.service"
  SUBSYSTEM=="cpu", ACTION=="remove", PROGRAM="/bin/systemctl try-restart kdump-tools.service"

  Also, with how CPU hot add & remove are handled in ppc64, a udev trigger
  to reload kdump after CPU is hot removed is NOT necessary. So, fix the CPU
  hot add case by updating the udev rule and drop the udev rule meant for CPU
  hot remove in the kdump udev rules file:

  
  SUBSYSTEM=="cpu", ACTION=="online", PROGRAM="/bin/systemctl try-restart kdump-tools.service"

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