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[Brad Figg <brad.figg@xxxxxxxxxxxxx>]

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** Changed in: linux (Ubuntu)
       Status: New => Confirmed

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https://bugs.launchpad.net/bugs/1552752

Title:
  kernel bug when mounting a qemu-nbd backed image

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  
  1. % lsb_release -rd
  Description:	Ubuntu 15.10
  Release:	15.10

  2. 
  % apt-cache policy linux-image-generic
  linux-image-generic:
    Installed: (none)
    Candidate: 4.2.0.30.33
    Version table:
       4.2.0.30.33 0
          500 http://us.archive.ubuntu.com/ubuntu/ wily-updates/main amd64 Packages
          500 http://security.ubuntu.com/ubuntu/ wily-security/main amd64 Packages
       4.2.0.16.18 0
          500 http://us.archive.ubuntu.com/ubuntu/ wily/main amd64 Packages

  (kriek) ~ % apt-cache policy qemu-utils
  qemu-utils:
    Installed: 1:2.3+dfsg-5ubuntu9.2
    Candidate: 1:2.3+dfsg-5ubuntu9.2
    Version table:
   *** 1:2.3+dfsg-5ubuntu9.2 0
          500 http://us.archive.ubuntu.com/ubuntu/ wily-updates/main amd64 Packages
          500 http://security.ubuntu.com/ubuntu/ wily-security/main amd64 Packages
          100 /var/lib/dpkg/status
       1:2.3+dfsg-5ubuntu9 0
          500 http://us.archive.ubuntu.com/ubuntu/ wily/main amd64 Packages

  
  3. Configure an NBD device with a qemu image and then mount it.  The base image is a wily amd64 cloud-image in raw format.
  Created the qcow2 device with: qemu-img create -f qcow2 -b /path/to/cloud-image.raw boot.img 2G
  Connect to nbd: sudo qemu-nbd -c /dev/nbd0 boot.img
  Mount it: sudo mount /dev/nbd0 /mnt
  Mount succeeds and I can examine the image.

  % qemu-img info --backing-chain boot.img 
  image: boot.img
  file format: qcow2
  virtual size: 2.0G (2147483648 bytes)
  disk size: 196K
  cluster_size: 65536
  backing file: /srv/images/wily/amd64/20160218/vmtest.root-image
  Format specific information:
      compat: 1.1
      lazy refcounts: false
      refcount bits: 16
      corrupt: false

  image: /srv/images/wily/amd64/20160218/vmtest.root-image
  file format: raw
  virtual size: 1.4G (1468006400 bytes)
  disk size: 1.4G

  4.  mount command hung and kernel emitted BUG().
  In reproducing this may be relevant.

  a. Configure NBD with boot.img as in (3)
  b. while still mounted rm boot.img
  c. disconnect: qemu-nbd -d /dev/nbd0
  d. unmount: umount /mnt

  Then repeat (3).

  ProblemType: Bug
  DistroRelease: Ubuntu 15.10
  Package: linux-image-4.2.0-19-generic 4.2.0-19.23
  ProcVersionSignature: Ubuntu 4.2.0-19.23-generic 4.2.6
  Uname: Linux 4.2.0-19-generic x86_64
  AlsaVersion: Advanced Linux Sound Architecture Driver Version k4.2.0-19-generic.
  AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
  ApportVersion: 2.19.1-0ubuntu5
  Architecture: amd64
  ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', '/dev/snd/hwC0D3', '/dev/snd/pcmC0D8p', '/dev/snd/pcmC0D7p', '/dev/snd/pcmC0D3p', '/dev/snd/controlC0', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
  Card0.Amixer.info: Error: [Errno 2] No such file or directory: 'amixer'
  Card0.Amixer.values: Error: [Errno 2] No such file or directory: 'amixer'
  Date: Thu Mar  3 09:18:14 2016
  HibernationDevice: RESUME=/dev/mapper/kriek--vg-swap_1
  InstallationDate: Installed on 2015-05-10 (297 days ago)
  InstallationMedia: Ubuntu-Server 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.3)
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.2.0-19-generic root=/dev/mapper/hostname--vg-root ro nomdmonddf nomdmonisw
  RelatedPackageVersions:
   linux-restricted-modules-4.2.0-19-generic N/A
   linux-backports-modules-4.2.0-19-generic  N/A
   linux-firmware                            1.149.3
  RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 11/05/2014
  dmi.bios.vendor: Intel Corp.
  dmi.bios.version: RKPPT10H.86A.0037.2014.1105.1813
  dmi.board.asset.tag: To be filled by O.E.M.
  dmi.board.name: D53427RKE
  dmi.board.vendor: Intel Corporation
  dmi.board.version: G87971-406
  dmi.chassis.type: 3
  dmi.modalias: dmi:bvnIntelCorp.:bvrRKPPT10H.86A.0037.2014.1105.1813:bd11/05/2014:svn:pn:pvr:rvnIntelCorporation:rnD53427RKE:rvrG87971-406:cvn:ct3:cvr:

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