Error stacktrace:

2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi [req-8ec61501-fe65-4b1b-a8af-ab71bbc15393 0d671b302f6a4aa29dd605881a9ac7e7 88bccf10385a45d0a8cd0733e5db8734 - 1e1b967db9714f78a63a26eabccc312d 1e1b967db9714f78a63a26eabccc312d] Caught error: error unprotecting snapshot 56d1c793-2d91-4aae-bc77-37f4fc0f38b5@snap 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi Traceback (most recent call last): 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/common/wsgi.py", line 1113, in __call__ 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     request, **action_args) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/common/wsgi.py", line 1152, in dispatch 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     return method(*args, **kwargs) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/common/utils.py", line 363, in wrapped 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     return func(self, req, *args, **kwargs) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/api/v2/images.py", line 235, in delete 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     image.delete() 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/domain/proxy.py", line 186, in delete 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     self.base.delete() 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/domain/proxy.py", line 186, in delete 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     self.base.delete() 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/api/policy.py", line 163, in delete 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     return self.image.delete() 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/domain/proxy.py", line 186, in delete 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     self.base.delete() 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/location.py", line 407, in delete 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     location) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/common/store_utils.py", line 114, in delete_image_location_from_backend 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     safe_delete_from_backend(context, image_id, location) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance/common/store_utils.py", line 48, in safe_delete_from_backend 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     ret = store_api.delete_from_backend(location['url'], context=context) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance_store/backend.py", line 372, in delete_from_backend 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     return store.delete(loc, context=context) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance_store/capabilities.py", line 225, in op_checker 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     return store_op_fun(store, *args, **kwargs) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance_store/_drivers/rbd.py", line 531, in delete 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     self._delete_image(target_pool, loc.image, loc.snapshot) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "/usr/lib/python2.7/dist-packages/glance_store/_drivers/rbd.py", line 392, in _delete_image 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi     image.unprotect_snap(snapshot_name) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi   File "rbd.pyx", line 1486, in rbd.Image.unprotect_snap (/build/ceph-10.2.6/src/build/rbd.c:15199) 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi InvalidArgument: error unprotecting snapshot 56d1c793-2d91-4aae-bc77-37f4fc0f38b5@snap 
2017-04-25 10:15:26.646 11926 ERROR glance.common.wsgi