Darren, I just checked the code, you are right. In case of one thread throws exception in downloading template to primary, it will delete the entry in template_store_ref, causing the second thread failing with NPE. We need to fix this in 4.3. Please file a bug for this.
Thanks -min From: Darren Shepherd <darren.s.sheph...@gmail.com<mailto:darren.s.sheph...@gmail.com>> Date: Thursday, October 31, 2013 11:39 AM To: "dev@cloudstack.apache.org<mailto:dev@cloudstack.apache.org>" <dev@cloudstack.apache.org<mailto:dev@cloudstack.apache.org>>, Min Chen <min.c...@citrix.com<mailto:min.c...@citrix.com>> Subject: race conditions in VolumeServiceImpl.createBaseImageAsync() creates NPE The following code results in a NPE in bad situations templatePoolRef = _tmpltPoolDao.acquireInLockTable(templatePoolRefId, storagePoolMaxWaitSeconds); if (templatePoolRef == null) { if (s_logger.isDebugEnabled()) { s_logger.info<http://s_logger.info>("Unable to acquire lock on VMTemplateStoragePool " + templatePoolRefId); } templatePoolRef = _tmpltPoolDao.findByPoolTemplate(dataStore.getId(), template.getId()); if (templatePoolRef.getState() == ObjectInDataStoreStateMachine.State.Ready ) { s_logger.info<http://s_logger.info>("Unable to acquire lock on VMTemplateStoragePool " + templatePoolRefId + ", But Template " + template.getUniqueName() + " is already copied to primary storage, skip copying"); createVolumeFromBaseImageAsync(volume, templateOnPrimaryStoreObj, dataStore, future); return; } throw new CloudRuntimeException("Unable to acquire lock on VMTemplateStoragePool: " + templatePoolRefId); } If two threads are trying to stage the same template thread one gets the lock, thread two will wait. If thread one fails to stage the template it will delete the templatePoolRef from the database. Thread two will now get the lock in op_lock, but the internal findById will not find a templatePoolRef because it has been deleted and return null from acquireInLockTable(). Technically thread two has the lock, but the ref templatePoolRef wasn't found. The subsequent line "templatePoolRef = _tmpltPoolDao.findByPoolTemplate(...)" will return null, because it doesn't exist and then on the next line templatePoolRef.getState() will throw a NPE. Darren
