[lxc-devel] issue with cgroups on very first start of any container after bootstrapping the host

[Jäkel, Guido]

Hello Developers,

using Gentoo's   lxc-0.8.0_rc1-r4  with a Kernel  gentoo-sources-3.3.5  I observe the following issue concerning the cgroupfs:

For reasons of compatibility I have still mounted the controllers of the cgroupfs at a single mountpoint  /cgroup/ . 

	# grep cgroup /etc/fstab:
	cgroup                  /cgroup         cgroup          defaults        0 0

After a bootstrap of the host this shows up as

	# grep cgroup /proc/mounts 
	cgroup /cgroup cgroup rw,relatime,blkio,freezer,devices,memory,cpuacct,cpu,cpuset 0 0    



If I now try to start the first container, it will fail  (for *any* previous well working container). The important messages in the log are:


      lxc-start 1340194612.650 INFO     lxc_cgroup - [1] found cgroup mounted at '/cgroup',opts='rw,relatime,blkio,freezer,devices,memory,cpuacct,cpu,cpuset'
      lxc-start 1340194612.650 DEBUG    lxc_cgroup - get_init_cgroup: found init cgroup for subsys (null) at /


      lxc-start 1340194612.650 DEBUG    lxc_cgroup - cgroup /cgroup has flags 0x0
      lxc-start 1340194612.682 INFO     lxc_cgroup - created cgroup '/cgroup//lxc/testcat0'
      lxc-start 1340194612.682 DEBUG    lxc_cgroup - checking '/proc/bus/usb' (usbfs)
      lxc-start 1340194612.683 DEBUG    lxc_conf - move '(null)' to '10591'
      lxc-start 1340194612.762 DEBUG    lxc_start - Dropped cap_sys_boot

      lxc-start 1340194612.762 INFO     lxc_conf - '' hostname has been setup
      lxc-start 1340194612.792 DEBUG    lxc_conf - mac address '00:50:C2:45:3C:14' on 'eth0' has been setup
      lxc-start 1340194612.795 DEBUG    lxc_conf - 'eth0' has been setup
      lxc-start 1340194612.795 INFO     lxc_conf - network has been setup
      lxc-start 1340194612.795 DEBUG    lxc_conf - mounted '/etc/lxc/testcat0/rootfs' on '/usr/lib/lxc/rootfs'
	[...]
      lxc-start 1340194612.797 INFO     lxc_conf - mount points have been setup
      lxc-start 1340194612.798 ERROR    lxc_conf - No such file or directory - failed to mount '/cgroup/testcat0' on '/usr/lib/lxc/rootfs/cgroup'  <<-- SHOULD BE /cgroup/lxc/testcat0  HERE ???
      lxc-start 1340194612.798 ERROR    lxc_conf - failed to setup the mount entries for 'testcat0'
      lxc-start 1340194612.798 ERROR    lxc_start - failed to setup the container
      lxc-start 1340194612.798 ERROR    lxc_sync - invalid sequence number 1. expected 2
      lxc-start 1340194612.799 ERROR    lxc_start - failed to spawn 'testcat0'
      lxc-start 1340194612.799 DEBUG    lxc_cgroup - get_init_cgroup: found init cgroup for subsys (null) at /


      lxc-start 1340194612.799 DEBUG    lxc_cgroup - destroying /cgroup//lxc/testcat0

      lxc-start 1340194612.858 DEBUG    lxc_cgroup - '/cgroup//lxc/testcat0' unlinked




After this first try, there is the new lxc super directory  /cgroups/lxc  and the mount options of the cgroupfs now show an additional  clone_childern

	cgroup /cgroup cgroup rw,relatime,blkio,freezer,devices,memory,cpuacct,cpu,cpuset,clone_children 0 0    

respectively  /cgroup/cgroup.clone_children  is 1.


As from now, starting of the containers will work:

      lxc-start 1340194763.755 INFO     lxc_cgroup - [1] found cgroup mounted at '/cgroup',opts='rw,relatime,blkio,freezer,devices,memory,cpuacct,cpu,cpuset,clone_children'
      lxc-start 1340194763.755 DEBUG    lxc_cgroup - get_init_cgroup: found init cgroup for subsys (null) at /


      lxc-start 1340194763.755 DEBUG    lxc_cgroup - cgroup /cgroup has flags 0x0
      lxc-start 1340194763.798 INFO     lxc_cgroup - created cgroup '/cgroup//lxc/testcat0'
      lxc-start 1340194763.798 DEBUG    lxc_cgroup - checking '/proc/bus/usb' (usbfs)
      lxc-start 1340194763.799 DEBUG    lxc_conf - move '(null)' to '10730'
      lxc-start 1340194763.858 DEBUG    lxc_start - Dropped cap_sys_boot

      lxc-start 1340194763.858 INFO     lxc_conf - '' hostname has been setup
      lxc-start 1340194763.900 DEBUG    lxc_conf - mac address '00:50:C2:45:3C:14' on 'eth0' has been setup
      lxc-start 1340194763.904 DEBUG    lxc_conf - 'eth0' has been setup
      lxc-start 1340194763.904 INFO     lxc_conf - network has been setup
      lxc-start 1340194763.904 DEBUG    lxc_conf - mounted '/etc/lxc/testcat0/rootfs' on '/usr/lib/lxc/rootfs'
	[...]
      lxc-start 1340194763.905 INFO     lxc_conf - mount points have been setup
      lxc-start 1340194763.906 DEBUG    lxc_conf - remounting /cgroup/lxc/testcat0 on /usr/lib/lxc/rootfs/cgroup to respect bind or remount options
      lxc-start 1340194763.906 DEBUG    lxc_conf - mounted '/cgroup/lxc/testcat0' on '/usr/lib/lxc/rootfs/cgroup', type 'none'
      lxc-start 1340194763.906 INFO     lxc_conf - mount points have been setup
      lxc-start 1340194763.906 DEBUG    lxc_cgroup - lxc_cgroup_path_get: called for subsys devices name testcat0

      lxc-start 1340194763.907 DEBUG    lxc_cgroup - using cgroup mounted at '/cgroup/lxc'
      lxc-start 1340194763.907 DEBUG    lxc_cgroup - lxc_cgroup_path_get: returning /cgroup/lxc/testcat0 for subsystem devices.deny
      lxc-start 1340194763.907 DEBUG    lxc_conf - cgroup 'devices.deny' set to 'a'
      lxc-start 1340194763.907 DEBUG    lxc_cgroup - lxc_cgroup_path_get: called for subsys devices name testcat0


If manually clear or set  /cgroup/cgroup.clone_children  and delete/create  /cgroup/lxc  it shows, that especial the absence of the lxc super-directory will reproduce the issue. It will be created by the first start of lxc afterwards (and never removed afterwards), but not yet used in this run. Therefore, a quick workaround is to create it in the host init scripts.



greetings

Guido