Merge pull request #3989 from matrix-org/rav/better_stacktraces

Avoid reraise, to improve stacktraces

changelog.d/3989.misc

@@ -0,0 +1 @@
+Improve stacktraces in certain exceptions in the logs

synapse/handlers/federation.py

@@ -18,7 +18,6 @@
 
 import itertools
 import logging
-import sys
 
 import six
 from six import iteritems, itervalues
@@ -1602,6 +1601,9 @@ class FederationHandler(BaseHandler):
             auth_events=auth_events,
         )
 
+        # reraise does not allow inlineCallbacks to preserve the stacktrace, so we
+        # hack around with a try/finally instead.
+        success = False
         try:
             if not event.internal_metadata.is_outlier() and not backfilled:
                 yield self.action_generator.handle_push_actions_for_event(
@@ -1612,16 +1614,14 @@ class FederationHandler(BaseHandler):
                 [(event, context)],
                 backfilled=backfilled,
             )
-        except:  # noqa: E722, as we reraise the exception this is fine.
+            success = True
-            tp, value, tb = sys.exc_info()
+        finally:
-
+            if not success:
                 logcontext.run_in_background(
                     self.store.remove_push_actions_from_staging,
                     event.event_id,
                 )
 
-            six.reraise(tp, value, tb)
-
         defer.returnValue(context)
 
     @defer.inlineCallbacks

synapse/handlers/message.py

@@ -14,9 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-import sys
 
-import six
 from six import iteritems, itervalues, string_types
 
 from canonicaljson import encode_canonical_json, json
@@ -624,6 +622,9 @@ class EventCreationHandler(object):
             event, context
         )
 
+        # reraise does not allow inlineCallbacks to preserve the stacktrace, so we
+        # hack around with a try/finally instead.
+        success = False
         try:
             # If we're a worker we need to hit out to the master.
             if self.config.worker_app:
@@ -636,6 +637,7 @@ class EventCreationHandler(object):
                     ratelimit=ratelimit,
                     extra_users=extra_users,
                 )
+                success = True
                 return
 
             yield self.persist_and_notify_client_event(
@@ -645,18 +647,17 @@ class EventCreationHandler(object):
                 ratelimit=ratelimit,
                 extra_users=extra_users,
             )
-        except:  # noqa: E722, as we reraise the exception this is fine.
+
+            success = True
+        finally:
+            if not success:
                 # Ensure that we actually remove the entries in the push actions
                 # staging area, if we calculated them.
-            tp, value, tb = sys.exc_info()
-
                 run_in_background(
                     self.store.remove_push_actions_from_staging,
                     event.event_id,
                 )
 
-            six.reraise(tp, value, tb)
-
     @defer.inlineCallbacks
     def persist_and_notify_client_event(
         self,