Created attachment 1192813 [details]
engine log

Description of problem:

Setup:
rhevm-4.0.2.7-0.1.el7ev.noarch
DC-Cluster 3.6 with 2 hosts with: vdsm-4.17.33-1.
Created a rhel-7.2 vm set to custom cluster compatibility 3.6, vm has 1 cpu.
Upgraded the hosts to 4.0: vdsm-4.18.11-1.el7ev.x86_64 , one by one (migrating the vm between them).
Finally upgraded the cluster and dc to 4.0 successfully.
After upgrade vm is marked to reboot and still has custom cluster compatibility 3.6.
Trying to hotplug another cpu (setting sockets to 2) fails with an error:
"Failed to hot set number of CPUS to VM test-vm-clone-2. Underlying error message: Hot plugging a CPU is not supported for cluster version 3.6 and architecture x86_64"

From engine.log

2016-08-21 18:14:17,988 ERROR [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (default task-11) [72e82ba8] Correlation ID: null, Call Stack: null, Custom Event ID: -1, Message: Failed to hot set number of CPUS to VM test-vm-clone-2. Underlying error message: Hot plugging a CPU is not supported for cluster version 3.6 and architecture x86_64.
2016-08-21 18:14:18,020 INFO  [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (default task-11) [72e82ba8] Correlation ID: 299904bb, Job ID: 39186ef5-a619-422e-94dd-b74981887871, Call Stack: null, Custom Event ID: -1, Message: VM test-vm-clone-2 configuration was updated by admin@internal-authz.
2016-08-21 18:14:18,025 INFO  [org.ovirt.engine.core.bll.UpdateVmCommand] (default task-11) [72e82ba8] Lock freed to object 'EngineLock:{exclusiveLocks='[test-vm-clone-2=<VM_NAME, ACTION_TYPE_FAILED_VM_IS_BEING_UPDATED>]', sharedLocks='[fc68f70c-792b-4006-9d64-8887fd716036=<VM, ACTION_TYPE_FAILED_VM_IS_BEING_UPDATED>]'}'

Version-Release number of selected component (if applicable):
rhevm-4.0.2.7-0.1.el7ev.noarch

How reproducible:
re produced with several vms.

Steps to Reproduce:
as mentioned above.

Actual results:
Fails to add cpu to vm.

Expected results:
cpu is added to vm instantly.

Additional info: