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[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

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

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https://bugs.launchpad.net/bugs/1793464

Title:
  Kernel panic after the ubuntu_nbd_smoke_test on Xenial kernel

Status in ubuntu-kernel-tests:
  New
Status in linux package in Ubuntu:
  In Progress
Status in linux source package in Xenial:
  New

Bug description:
  == SRU Justification ==

  When running the Ubuntu nbd autotest regression test we trip a hang
  and then a little later a panic message.  There are two upstream
  fixes required as this is actually two issues in one. One fix is to 
  not to shutdown the sock when IRQs are disable and a second to fix is
  to race in the nbd ioctl.

  == Fix ==

  Upstream commits:

  23272a6754b81ff6503e09c743bb4ceeeab39997
    nbd: Remove signal usage

  1f7b5cf1be4351e60cf8ae7aab976503dd73c5f8
    nbd: Timeouts are not user requested disconnects

  0e4f0f6f63d3416a9e529d99febfe98545427b81
    nbd: Cleanup reset of nbd and bdev after a disconnect

  c261189862c6f65117eb3b1748622a08ef49c262
    nbd: don't shutdown sock with irq's disabled

  97240963eb308d8d21a89c0459822f7ea98463b4
    nbd: fix race in ioctl

  The first 3 patches are prerequisites required for the latter two fixes to apply and work correctly.  Most of these backports are minor patch wiggles
  required because later patches have been applied to the driver in earlier fixes to this driver.
     

  == Regression Potential ==

  These fixes just touch nbd, so the regression potential is just
  limited to this. Secondly, we are pulling in upstream fixes that exist
  in Bionic and Cosmic kernels, so these are tried and tested fixes.

  == Test Case ==

    1. Deploy a node with 4.4 Xenial
    2. Run the ubuntu_nbd_smoke_test

  Without the fix, we get hang/crashes.  With the fix one can run this test
  multiple times without any issues at all.

  
  ----

  This issue can be reproduced on AMD64 KVM //bare-metal node, s390x
  zKVM node

  The test itself will pass, but the system will hang after a few
  second.

  Steps:
    1. Deploy a node with 4.4 Xenial
    2. Run the ubuntu_nbd_smoke_test

  If you have access to the console, you will see that this system
  actually bumped into a kernel panic:

   Unable to handle kernel pointer dereference in virtual kernel address space
   failing address: 000003ff802c1000 TEID: 000003ff802c1803
   Fault in home space mode while using kernel ASCE.
   Log here (s390x KVM): https://pastebin.ubuntu.com/p/dNmtvbGjmz/

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: linux-image-4.4.0-136-generic 4.4.0-136.162
  ProcVersionSignature: Ubuntu 4.4.0-136.162-generic 4.4.144
  Uname: Linux 4.4.0-136-generic s390x
  NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
  AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: cannot access '/dev/snd/': No such file or directory
  AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
  ApportVersion: 2.20.1-0ubuntu2.18
  Architecture: s390x
  ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
  CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found.
  Date: Thu Sep 20 03:46:00 2018
  HibernationDevice: RESUME=UUID=ca468a9c-9563-442c-85c6-6055e800a66e
  IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
  Lspci:

  Lsusb: Error: command ['lsusb'] failed with exit code 1:
  PciMultimedia:

  ProcFB: Error: [Errno 2] No such file or directory: '/proc/fb'
  ProcKernelCmdLine: root=UUID=b65b756a-ba4e-4c53-aa32-0db2bdb50bb3 crashkernel=196M
  RelatedPackageVersions:
   linux-restricted-modules-4.4.0-136-generic N/A
   linux-backports-modules-4.4.0-136-generic  N/A
   linux-firmware                             1.157.20
  RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)

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