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[Bug 1292234] Re: qcow2 image corruption on non-extent filesystems (ext3)

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Apparently this bug is also present in Debian. In my case the corrupted
image was a windows one. When I run qemu-img check over it it will
complain about lots of clusters, and if I pass it the repair flag, then
it will end up crashing with the following message:

$  qemu-img check -r all windows.img
Repairing cluster 0 refcount=0 reference=1
Repairing cluster 1 refcount=0 reference=1
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
Repairing cluster 2 refcount=0 reference=1
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
Repairing cluster 3 refcount=0 reference=1
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
Repairing cluster 4 refcount=0 reference=1
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
Repairing cluster 5 refcount=0 reference=1
qcow2: Preventing invalid write on metadata (overlaps with active L1 table); image marked as corrupt.
Repairing cluster 6 refcount=0 reference=1
...
Repairing OFLAG_COPIED data cluster: l2_entry=8000000397a59000 refcount=0
Repairing OFLAG_COPIED data cluster: l2_entry=8000000397a5a000 refcount=0
Repairing OFLAG_COPIED data cluster: l2_entry=800000000001b000 refcount=0
The following inconsistencies were found and repaired:

    0 leaked clusters
    97850 corruptions

Double checking the fixed image now...
[1]    27716 segmentation fault (core dumped)  qemu-img check -r all windows.img


Has anyone else tried this over a copy of the corrupted image?

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https://bugs.launchpad.net/bugs/1292234

Title:
  qcow2 image corruption on non-extent filesystems (ext3)

Status in linux package in Ubuntu:
  In Progress
Status in qemu package in Ubuntu:
  Invalid

Bug description:
  [Impact]
  Users of non-extent ext4 filesystems (ext4 ^extents, or ext3 w/ CONFIG_EXT4_USE_FOR_EXT23=y) can encounter data corruption when using fallocate with FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE flags. This seems to be a regression in ext4_ind_remove_space introduced in 4f579ae7, whereas commit 77ea2a4b passes the following test case.

  [Test Case]
  1) Setup ext4 ^extents, or ext3 filesystem with CONFIG_EXT4_USE_FOR_EXT23=y
  2) Create and install a VM using a qcow2 image and store the file on the filesystem
  3) Snapshot the image with qemu-img
  4) Boot the image and do some disk operations (fio,etc)
  5) Shutdown image and delete snapshot
  6) Repeat 3-5 until VM no longer boots due to image corruption, generally this takes a few iterations depending on disk operations.

  
  --

  The security team uses a tool (http://bazaar.launchpad.net/~ubuntu-
  bugcontrol/ubuntu-qa-tools/master/view/head:/vm-tools/uvt) that uses
  libvirt snapshots quite a bit. I noticed after upgrading to trusty
  some time ago that qemu 1.7 (and the qemu 2.0 in the candidate ppa)
  has had stability problems such that the disk/partition table seems to
  be corrupted after removing a libvirt snapshot and then creating
  another with the same name. I don't have a very simple reproducer, but
  had enough that hallyn suggested I file a bug. First off:

  qemu-kvm 2.0~git-20140307.4c288ac-0ubuntu2

  $ cat /proc/version_signature
  Ubuntu 3.13.0-16.36-generic 3.13.5

  $ qemu-img info ./forhallyn-trusty-amd64.img
  image: ./forhallyn-trusty-amd64.img
  file format: qcow2
  virtual size: 8.0G (8589934592 bytes)
  disk size: 4.0G
  cluster_size: 65536
  Format specific information:
      compat: 0.10

  Steps to reproduce:
  1. create a virtual machine. For a simplified reproducer, I used virt-manager with:
    OS type: Linux
    Version: Ubuntu 14.04
    Memory: 768
    CPUs: 1

    Select managed or existing (Browse, new volume)
      Create a new storage volume:
        qcow2
        Max capacity: 8192
        Allocation: 0

    Advanced:
      NAT
      kvm
      x86_64
      firmware: default

  2. install a VM. I used trusty-desktop-amd64.iso from Jan 23 since it
  seems like I can hit the bug more reliably if I have lots of updates
  in a dist-upgrade. I have seen this with lucid-trusty guests that are
  i386 and amd64. After the install, reboot and then cleanly shutdown

  3. Backup the image file somewhere since steps 1 and 2 take a while :)

  4. Execute the following commands which are based on what our uvt tool
  does:

  $ virsh snapshot-create-as forhallyn-trusty-amd64 pristine "uvt snapshot"
  $ virsh snapshot-current --name forhallyn-trusty-amd64
  pristine
  $ virsh start forhallyn-trusty-amd64
  $ virsh snapshot-list forhallyn-trusty-amd64 # this is showing as shutoff after start, this might be different with qemu 1.5

  in guest:
  sudo apt-get update
  sudo apt-get dist-upgrade
  780 upgraded...
  shutdown -h now

  $ virsh snapshot-delete forhallyn-trusty-amd64 pristine --children
  $ virsh snapshot-create-as forhallyn-trusty-amd64 pristine "uvt snapshot"

  $ virsh start forhallyn-trusty-amd64 # this command works, but there
  is often disk corruption

  The idea behind the above is to create a new VM with a pristine
  snapshot that we could revert later if we wanted. Instead, we boot the
  VM, run apt-get dist-upgrade, cleanly shutdown and then remove the old
  'pristine' snapshot and create a new 'pristine' snapshot. The
  intention is to update the VM and the pristine snapshot so that when
  we boot the next time, we boot from the updated VM and can revert back
  to the updated VM.

  After running 'virsh start' after doing snapshot-delete/snapshot-
  create-as, the disk may be corrupted. This can be seen with grub
  failing to find .mod files, the kernel not booting, init failing, etc.

  This does not seem to be related to the machine type used. Ie, pc-
  i440fx-1.5, pc-i440fx-1.7 and pc-i440fx-2.0 all fail with qemu 2.0,
  pc-i440fx-1.5 and pc-i440fx-1.7 fail with qemu 1.7 and pc-i440fx-1.5
  works fine with qemu 1.5.

  Only workaround I know if is to downgrade qemu to 1.5.0+dfsg-
  3ubuntu5.4 from Ubuntu 13.10.

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