cinder-volume cannot convert image to volume or volume to image when volume_copy_bps_limit option is greater than 0.

Issue

• cinder-volume cannot convert image to volume or volume to image when volume_copy_bps_limit option is greater than 0.
• cinder-volume.log contains the following exception.

DEBUG oslo_concurrency.processutils [req-XXX - - - - -] Running cmd (subprocess): cgcreate -g b
e /usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py:372
DEBUG oslo_concurrency.processutils [req-XXX - - - - -] u'cgcreate -g blkio:cinder-volume-copy'
 /usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py:457
ERROR oslo_service.service [req-XXX - - - - -] Error starting thread.: OSError: [Errno 2] No su

ERROR oslo_service.service Traceback (most recent call last):
ERROR oslo_service.service   File "/usr/lib/python2.7/site-packages/oslo_service/service.py", line 731, in run_service
ERROR oslo_service.service     service.start()
ERROR oslo_service.service   File "/usr/lib/python2.7/site-packages/cinder/service.py", line 225, in start
ERROR oslo_service.service     service_id=Service.service_id)
ERROR oslo_service.service   File "/usr/lib/python2.7/site-packages/cinder/volume/manager.py", line 500, in init_host
ERROR oslo_service.service     self.driver.set_throttle()
ERROR oslo_service.service   File "/usr/lib/python2.7/site-packages/cinder/volume/driver.py", line 522, in set_throttle
ERROR oslo_service.service     cgroup_name)
ERROR oslo_service.service   File "/usr/lib/python2.7/site-packages/cinder/volume/throttling.py", line 69, in __init__
ERROR oslo_service.service     run_as_root=True)
ERROR oslo_service.service   File "/usr/lib/python2.7/site-packages/cinder/utils.py", line 126, in execute
ERROR oslo_service.service     return processutils.execute(*cmd, **kwargs)
ERROR oslo_service.service   File "/usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py", line 391, in execute
ERROR oslo_service.service     env=env_variables)
ERROR oslo_service.service   File "/usr/lib/python2.7/site-packages/eventlet/green/subprocess.py", line 55, in __init__
ERROR oslo_service.service     subprocess_orig.Popen.__init__(self, args, 0, *argss, **kwds)
ERROR oslo_service.service   File "/usr/lib64/python2.7/subprocess.py", line 711, in __init__
ERROR oslo_service.service     errread, errwrite)
ERROR oslo_service.service   File "/usr/lib64/python2.7/subprocess.py", line 1327, in _execute_child
ERROR oslo_service.service     raise child_exception
ERROR oslo_service.service OSError: [Errno 2] No such file or directory
ERROR oslo_service.service