Do not refuse to set read_marker if previous is in wrong room

When the old read marker location happens to be an event_id in a
different room, we should not let this prevent a new read marker
from being set.

changelog.d/16990.bugfix

@@ -0,0 +1 @@
+Fix case in which `m.fully_read` marker would not get updated.

synapse/handlers/read_marker.py

@@ -48,12 +48,12 @@ async def received_client_read_marker(
 
             should_update = True
             # Get event ordering, this also ensures we know about the event
-            event_ordering = await self.store.get_event_ordering(event_id)
+            event_ordering = await self.store.get_event_ordering(event_id, room_id)
 
             if existing_read_marker:
                 try:
                     old_event_ordering = await self.store.get_event_ordering(
-                        existing_read_marker["event_id"]
+                        existing_read_marker["event_id"], room_id
                     )
                 except SynapseError:
                     # Old event no longer exists, assume new is ahead. This may

synapse/storage/databases/main/events_worker.py

@@ -1989,16 +1989,18 @@ def get_deltas_for_stream_id_txn(
         return rows, to_token, True
 
     @cached(max_entries=5000)
-    async def get_event_ordering(self, event_id: str) -> Tuple[int, int]:
+    async def get_event_ordering(self, event_id: str, room_id: str) -> Tuple[int, int]:
         res = await self.db_pool.simple_select_one(
             table="events",
             retcols=["topological_ordering", "stream_ordering"],
-            keyvalues={"event_id": event_id},
+            keyvalues={"event_id": event_id, "room_id": room_id},
             allow_none=True,
         )
 
         if not res:
-            raise SynapseError(404, "Could not find event %s" % (event_id,))
+            raise SynapseError(
+                404, "Could not find event %s in room %s" % (event_id, room_id)
+            )
 
         return int(res[0]), int(res[1])