Add missing logger

synapse/metrics/background_process_metrics.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import logging
 import threading
 
 import six
@@ -23,6 +24,9 @@ from twisted.internet import defer
 
 from synapse.util.logcontext import LoggingContext, PreserveLoggingContext
 
+logger = logging.getLogger(__name__)
+
+
 _background_process_start_count = Counter(
     "synapse_background_process_start_count",
     "Number of background processes started",