lib/selection: be more careful with RO transactions

They probably couldn't hang open for long, as each client request
should cause some cache-searching and thus close it, and even with
queries stopping I haven't managed to find a case where it would be
left open but... it's nicer to clean up and it should be very cheap.

lib/selection.h

@@ -254,6 +254,9 @@ uint8_t *ip_to_bytes(const union inaddr *src, size_t len);
 
 /**
  * @internal Fetch per-address information from various sources.
+ *
+ * Note that this opens a RO cache transaction; the callee is responsible
+ * for its closing not too long afterwards (e.g. calling kr_cache_commit).
  */
 void update_address_state(struct address_state *state, union inaddr *address,
 			  size_t address_len, struct kr_query *qry);

lib/selection_forward.c

@@ -53,7 +53,7 @@ void forward_choose_transport(struct kr_query *qry,
 		default:
 			kr_assert(false);
 			*transport = NULL;
-			return;
+			goto cleanup;
 		}
 
 		struct address_state *addr_state = &local_state->addr_states[i];
@@ -94,6 +94,8 @@ void forward_choose_transport(struct kr_query *qry,
 		qry->flags.TCP = (*transport)->protocol == KR_TRANSPORT_TCP
 			      || (*transport)->protocol == KR_TRANSPORT_TLS;
 	}
+cleanup:
+	kr_cache_commit(&qry->request->ctx->cache);
 }
 
 void forward_error(struct kr_query *qry, const struct kr_transport *transport,

lib/selection_iter.c

@@ -127,6 +127,7 @@ static void unpack_state_from_zonecut(struct iter_local_state *local_state,
 		}
 	}
 	trie_it_free(it);
+	kr_cache_commit(&qry->request->ctx->cache);
 }
 
 static int get_valid_addresses(struct iter_local_state *local_state,