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[troy engel <troyengel@xxxxxxxxx>]

I confirm it's fixed in 3.19.0-031900, it's still broken in 14.04.02 LTS
with kernel 3.16.0-30-generic. With further testing, whatever is broken
was fixed between 3.18rc2 and 3.18rc3 kernels:

 Broken: 3.18.0-031800rc2 [1]
 Fixed: 3.18.0-031800rc3 [2]

The number of commits between these two is rather high making it
difficult to easily spot what may have fixed the bug; the diff from rc2
to rc3 is 621,132 bytes.  The test setup is easy - using VirtualBox,
create a new VM accepting all defaults. Install 14.04.02 LTS using all
defaults, all very generic. In all broken cases specifying "noautogroup"
on the kernel params bypasses the bug.

I was able to record a MKV @100fps and extract two PNG files showing the
best I can capture; it goes by so fast that even at 100fps I can't
capture a few missing lines.

[1] http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.18-rc2-vivid/
[2] http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.18-rc3-vivid/


** Attachment added: "screencap of crash, 1/2"
   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1422016/+attachment/4325063/+files/p2146.png

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https://bugs.launchpad.net/bugs/1422016

Title:
  Kernel panic during system boot with sched_autogroup_enabled = 0

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  # lsb_release -rd
  Description:	Ubuntu 14.04.1 LTS
  Release:	14.04

  # uname -a
  Linux napa 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

  A kernel panic occurs while disabling the automatic task group
  creation within /etc/sysctl.conf using "kernel.sched_autogroup_enabled
  = 0".

  After adding the "noautogroup" kernel parameter to GRUB, the system
  will boot without issue.

  I have attached a screen shot of the stack trace as I was unable to
  capture the stack trace using netconsole, linux-crashdump, and
  /var/log/kern.log. Oddly enough, while trying one last approach
  (serial console) to capture the full trace within virtual box using a
  host pipe and setting console=ttyS0, the system booted without issue
  and disabled automatic task group creation.

  According to
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1055222, a fix
  for the issue has hit the Precise kernel and should be released in
  3.2.0-36.

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