Public bug reported:
A data corruption bug exists in the LXC driver for libvirt, that has
just cost me a MySQL server.
Steps to reproduce:
- (for visualization only) In virt-manager add a connection to local lxc://
- create an LXC container, that has a loop-mounted image file and start it
- (for visualization only) the container shows as running in virt-manager
- systemctl stop libvirtd ; sleep 2 ; sync ; systemctl start libvirtd
- (for visualization only) the container shows as shut off in virt-manager
- The container no longer responds to network requests, has no attachable
console
- The loop mount does no longer show up on host-side "mount" output
BUT: losetup -a reveals, that a loop device is still attached to the
image file
BUT: In reality this loop device is still mounted, processes in the
container still access the file system
BUT: There is no way to unmount or free it - losetup -d ends without an
error but does nothing
- restart the container (virsh -c lxc:// start name-of-container or via
virt-manager)
THIS SHOULD NOT BE ALLOWED
- The image file is now twice mounted and corruption starts creeping in
- Depending on how long this state persists (in terms of IO), the damage can be
significant
When finally discovering the problem, the only way to unstick the
container is a reboot. This is the final nail in the coffin: The hidden
instance syncs AFTER the new instance, effectivly pushing back the past.
This can be quite nasty, if a libvirt restart results from an unattended
upgrade.
I do understand, that libvirt/LXC is deprecated - this strikes me as a rather
unsubtle way to push users to the newest incarnation, though.
In non-enterprisy environments (read SMB or NGO) virt-manager is often used as
a "power user" tool, and those end users are unwilling if not unable to use
different toolsets for containers and full-fledged VMs. And disabling
unattended upgrades in such an environment is inviting trouble.
** Affects: libvirt (Ubuntu)
Importance: Undecided
Status: New
** Package changed: udev (Ubuntu) => libvirt (Ubuntu)
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https://bugs.launchpad.net/bugs/1680997
Title:
Container file system corruption on libvirtd restart
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