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[Colin Ian King <1573062@xxxxxxxxxxxxxxxxxx>]

I don't see any evidence of a hang, just evidence of a machine being
power-cycled.

Apr 19 21:26:33 ubuntu kernel: [19749.994340] [45742]  1000 45742      369       18       6       3       14             0 stress-ng-brk
Apr 19 21:26:33 ubuntu kernel: [19749.994342] [45743]  1000 45743      369       18       6       3       14             0 stress-ng-brk
Apr 19 21:26:33 ubuntu kernel: [19749.994344] Out of memory: Kill process 45583 (stress-ng-brk) score 28 or sacrifice child
Apr 19 21:26:33 ubuntu kernel: [19749.994566] Killed process 45583 (stress-ng-brk) total-vm:7976960kB, anon-rss:7048512kB, file-rss:1152kB
Apr 20 14:28:33 binacle kernel: [    0.000000] opal: OPAL V3 detected !
Apr 20 14:28:33 binacle kernel: [    0.000000] Allocated 4980736 bytes for 2048 pacas at c00000000fb40000
Apr 20 14:28:33 binacle kernel: [    0.000000] Using PowerNV machine description
Apr 20 14:28:33 binacle kernel: [    0.000000] Page sizes from device-tree:
Apr 20 14:28:33 binacle kernel: [    0.000000] base_shift=12: shift=12, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=0
Apr 20 14:28:33 binacle kernel: [    0.000000] base_shift=12: shift=16, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=7
Apr 20 14:28:33 binacle kernel: [    0.000000] base_shift=12: shift=24, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=56
Apr 20 14:28:33 binacle kernel: [    0.000000] base_shift=16: shift=16, sllp=0x0110, avpnm=0x00000000, tlbiel=1, penc=1

Can you supply details of how stress-ng is being run?

For this brk stressor test, stress-ng performs rapid heap expansion
using the brk() system call, which will force the system to consume all
available memory and then transition into a swapping phase.   This can
lead to an apparent "hung" situation (for example, your shell may be
swapped out), even though it is still active and not crashed.

The kernel messages you see in the kern.log are just the kernel OOM
killer killing off the best candidate process to free up memory;  this
free'd memory will be consumed rapidly again by other contending brk
stressors so the system will appear to be hung while it is busy cycling
around on the killing and spawning of these stressors.

Was the machine ping'able?  If so, it's not dead/hung.  Perhaps it got
power cycled prematurely.  What evidence was there that the machine was
hung?

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https://bugs.launchpad.net/bugs/1573062

Title:
  memory_stress_ng failing for IBM Power S812LC(TN71-BP012) for 16.04

Status in linux package in Ubuntu:
  Triaged

Bug description:
  memory_stress_ng, as part of server certification is failing for IBM
  Power S812LC(TN71-BP012) in bare metal mode. Failing in this case is
  defined by the test locking up the server in an unrecoverable state
  which only a reboot will fix.

  I will be attaching screen and kern logs for the failures and a
  successful run on 14.04 on the same server.

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