Same problem here with Gentoo guests.
Kernel : 2.6.32-4-pve
I can successfully online migrate a Debian guest, but not my Gentoo.
No informations found on Google, into vzctl source code, and with strace.
Can somebody inform us about the "get context..." operation, this would help to debug.
Starting online migration of CT 107 to 178.xxx.xxx.xxx
OpenVZ is running...
Loading /etc/vz/vz.conf and /etc/vz/conf/107.conf files
Check IPs on destination node: 46.xxx.xxx.xxx
Preparing remote node
Copying config file
107.conf 100% 1440 1.4KB/s 00:00
Saved parameters for CT 107
Creating remote container root dir
Creating remote container private dir
Initializing remote quota
Quota init
Turning remote quota on
Syncing private
Live migrating container...
Suspending container
Setting up checkpoint...
suspend...
get context...
Can not get context: File exists
Checkpointing failed
Error: Failed to suspend container