** Changed in: linux (Ubuntu Artful)
       Status: Fix Committed => In Progress

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  System hang with Linux kernel due to mainline commit 24247aeeabe

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Artful:
  In Progress
Status in linux source package in Bionic:
  Fix Committed

Bug description:
  == SRU Justification ==
  The following mainline commit introduced a regression in v4.14-rc1:
  24247aeeabe9 ("x86/intel_rdt/cqm: Improve limbo list processing")

  This commit made it's way into Artful via Launchpad bug 1591609 as Artful 

  This bug was causing regression tests to hang about one in four
  times when running cpu_offlining tests.

  This patch to fix this regression was just submitted to mainline, so it is 
  needed in Bionic.

  == Fix ==
  commit d47924417319e3b6a728c0b690f183e75bc2a702
  Author: Thomas Gleixner <t...@linutronix.de>
  Date:   Tue Jan 16 19:59:59 2018 +0100

      x86/intel_rdt/cqm: Prevent use after free

  == Regression Potential ==
  Low.  This patch fixes a current regression that is a use after free.

  ### Original Bug Description ###
  In doing Ubuntu 17.10 regression testing, we've encountered one computer 
(boldore, a Cisco UCS C240 M4 [VIC]), that hangs about one in four times when 
running our cpu_offlining test. This test attempts to take all the CPU cores 
offline except one, then brings them back online again. This test ran 
successfully on boldore with previous releases, but with 17.10, the system 
sometimes (about one in four runs) hangs. Reverting to Ubuntu 16.04.3, I found 
no problems; but when I upgraded the 16.04.3 installation to 
linux-image-4.13.0-16-generic, the problem appeared again, so I'm confident 
this is a problem with the kernel. I'm attaching two files, 
dmesg-output-4.10.txt and dmesg-output-4.13.txt, which show the dmesg output 
that appears when running the cpu_offlining test with 4.10.0-38 and 4.13.0-16 
kernels, respectively; the system hung on the 4.13 run. (I was running "dmesg 
-w" in a second SSH login; the files are cut-and-pasted from that.)

  I initiated this bug report from an Ubuntu 16.04.3 installation
  running a 4.10 kernel; but as I said, this applies to the 4.13 kernel.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: linux-image-4.10.0-38-generic 4.10.0-38.42~16.04.1
  ProcVersionSignature: User Name 4.10.0-38.42~16.04.1-generic 4.10.17
  Uname: Linux 4.10.0-38-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.10
  Architecture: amd64
  Date: Tue Nov 21 17:36:06 2017
   PATH=(custom, no user)
  SourcePackage: linux-hwe
  UpgradeStatus: No upgrade log present (probably fresh install)

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