1 files changed, 5 insertions, 0 deletions
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 08727e4857..1d0f6bcd6f 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1880,6 +1880,11 @@ class FederationHandler:
                 logger.info("Updating current state for %s", room_id)
                 # TODO(faster_joins): notify workers in notify_room_un_partial_stated
                 #   https://github.com/matrix-org/synapse/issues/12994
+                #
+                # NB: there's a potential race here. If room is purged just before we
+                # call this, we _might_ end up inserting rows into current_state_events.
+                # (The logic is hard to chase through.) We think this is fine, but if
+                # not the HS admin should purge the room again.
                 await self.state_handler.update_current_state(room_id)
 
                 logger.info("Handling any pending device list updates")