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Michal Privoznik ea7d0ca37c vircgroup: Fix virCgroupKillRecursive() wrt nested controllers
I've encountered the following bug, but only on Gentoo with
systemd and CGroupsV2. I've started an LXC container successfully
but destroying it reported the following error:

  error: Failed to destroy domain 'amd64'
  error: internal error: failed to get cgroup backend for 'pathOfController'

Debugging showed, that CGroup hierarchy is full of surprises:

/sys/fs/cgroup/machine.slice/machine-lxc\x2d861\x2damd64.scope/
└── libvirt
    ├── dev-hugepages.mount
    ├── dev-mqueue.mount
    ├── init.scope
    ├── sys-fs-fuse-connections.mount
    ├── sys-kernel-config.mount
    ├── sys-kernel-debug.mount
    ├── sys-kernel-tracing.mount
    ├── system.slice
    │   ├── console-getty.service
    │   ├── dbus.service
    │   ├── system-getty.slice
    │   ├── system-modprobe.slice
    │   ├── systemd-journald.service
    │   ├── systemd-logind.service
    │   └── tmp.mount
    └── user.slice

For comparison, here's the same container on recent Rawhide:

/sys/fs/cgroup/machine.slice/machine-lxc\x2d13550\x2damd64.scope/
└── libvirt

Anyway, those nested directories should not be a problem, because
virCgroupKillRecursiveInternal() removes them recursively, right?
Sort of. The function really does remove nested directories, but
it assumes that every directory has the same controller as the
rest. Just take a look at virCgroupV2KillRecursive() - it gets
'Any' controller (the first one it found in ".scope") and then
passes it to virCgroupKillRecursiveInternal().

This assumption is not true though. The controllers found in
".scope" are the following:

  cpuset cpu io memory pids

while "libvirt" has fewer:

  cpuset cpu io memory

Up until now it's not problem, because of how we order
controllers internally - "cpu" is the first and thus picking
"Any" controller returns just that. But the rest of directories
has no controllers, their "cgroup.controllers" is just empty.

What fixes the bug is dropping @controller argument from
virCgroupKillRecursiveInternal() and letting each iteration work
pick its own controller.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
2021-04-19 11:21:40 +02:00
2019-05-31 17:54:28 +02:00
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Libvirt API for virtualization

Libvirt provides a portable, long term stable C API for managing the virtualization technologies provided by many operating systems. It includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER Hypervisor.

For some of these hypervisors, it provides a stateful management daemon which runs on the virtualization host allowing access to the API both by non-privileged local users and remote users.

Layered packages provide bindings of the libvirt C API into other languages including Python, Perl, PHP, Go, Java, OCaml, as well as mappings into object systems such as GObject, CIM and SNMP.

Further information about the libvirt project can be found on the website:

https://libvirt.org

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Description
Libvirt provides a portable, long term stable C API for managing the virtualization technologies provided by many operating systems. It includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER Hypervisor.
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