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[Dirk Fleischer <Dirk.Fleischer@xxxxxxxxx>]

I did a little more testing.

root@virt:~# uname -r
3.13.0-32-generic


Actually the hanging seams to happen only when the overlayfs parts are on the logical volume being the snapshot source.
Let's say /opt is a logical volume in the volume group virt.

Case 1 (hanging):
mkdir /opt/test/
cd /opt/test/
mkdir upper lower file_system
touch lower/bla.dat

mount -t overlayfs -o lowerdir=/opt/test/lower,upperdir=/opt/test/upper
overlayfs /opt/test/file_system

lvcreate -s -L 5G /dev/virt/opt -n vm_backup

-> Hang (see previous posts)

Case 2 (not hanging):
mkdir /opt/test/
lvcreate -n test -L10G virt
mkfs.xfs /dev/virt/test
mount /dev/virt/test /opt/test
cd /opt/test/
mkdir upper lower file_system
touch lower/bla.dat
mount -t overlayfs -o lowerdir=/opt/test/lower,upperdir=/opt/test/upper overlayfs /opt/test/file_system
lvcreate -s -L 5G /dev/virt/opt -n vm_backup 

Snapshot created even through the overlayfs is in use (but  on a
different volume).

So the work around for the moment is to use two types of logical volumes :
1 one type for use with overlayfs where one has to make sure that no one ever takes a snapshot of (at least until this bug is fixed.)
2. one type where overlayfs never gets used but where snapshots can be taken from.

May be this helps someone running into this issue.

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https://bugs.launchpad.net/bugs/1328595

Title:
  lvcreate -s hangs when overlayfs is in use

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  I am using xbuntu 14.04 LTS in combination with KVM, lxc, logical volumes and overlayfs.
  After I started  using overlayfs i realized that my backup based on LVM snapshots made the system "go mad".

  As described in the manual I tried the kernel from 13.10 (3.11.0-xx) with the same result.
  A test against main line does not help, since it does not include the overlayfs support.

  I tested the behaviour on a server as well as in a VirtualBox environment with the same result:
  lvcreate -s -n backup -L512M /dev/VG/NAME hangs and does not come back.

  This issue is easy reproducable:

  sudo mkdir /mnt/test /mnt/delta
  sudo mount -t overlayfs -o lowerdir=/usr,upperdir=/mnt/delta overlayfs /mnt/test
  sudo lvcreate -s -n backup -L512M /dev/xubuntu-vg/root

  -> Hang
  df@feretti-virt:~$ uname -r
  3.13.0-29-generic

  df@feretti-virt:~$ cat /proc/version_signature 
  Ubuntu 3.13.0-29.53-generic 3.13.11.2

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-3.13.0-29-generic 3.13.0-29.53
  ProcVersionSignature: Ubuntu 3.13.0-29.53-generic 3.13.11.2
  Uname: Linux 3.13.0-29-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.2
  Architecture: amd64
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', '/dev/snd/controlC0', '/dev/snd/pcmC0D0c', '/dev/snd/pcmC0D0p', '/dev/snd/pcmC0D1c', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
  Date: Tue Jun 10 18:02:13 2014
  HibernationDevice: RESUME=UUID=6e68761a-6768-4e19-9c4e-f188538d6068
  InstallationDate: Installed on 2014-02-18 (112 days ago)
  InstallationMedia: Xubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016)
  Lsusb:
   Bus 001 Device 002: ID 80ee:0021 VirtualBox USB Tablet
   Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
  MachineType: innotek GmbH VirtualBox
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=de_DE.UTF-8
   SHELL=/bin/bash
  ProcFB: 0 VESA VGA
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.13.0-29-generic root=/dev/mapper/xubuntu--vg-root ro quiet splash vt.handoff=7
  PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon.
  RelatedPackageVersions:
   linux-restricted-modules-3.13.0-29-generic N/A
   linux-backports-modules-3.13.0-29-generic  N/A
   linux-firmware                             1.127.2
  RfKill:
   
  SourcePackage: linux
  UpgradeStatus: Upgraded to trusty on 2014-04-22 (49 days ago)
  dmi.bios.date: 12/01/2006
  dmi.bios.vendor: innotek GmbH
  dmi.bios.version: VirtualBox
  dmi.board.name: VirtualBox
  dmi.board.vendor: Oracle Corporation
  dmi.board.version: 1.2
  dmi.chassis.type: 1
  dmi.chassis.vendor: Oracle Corporation
  dmi.modalias: dmi:bvninnotekGmbH:bvrVirtualBox:bd12/01/2006:svninnotekGmbH:pnVirtualBox:pvr1.2:rvnOracleCorporation:rnVirtualBox:rvr1.2:cvnOracleCorporation:ct1:cvr:
  dmi.product.name: VirtualBox
  dmi.product.version: 1.2
  dmi.sys.vendor: innotek GmbH

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