migration: Make multifd_recv_terminate_threads() own the error

Make multifd_recv_terminate_threads() take ownership of the error always.
Paving way for making migrate_set_error() to take ownership.

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Link: https://lore.kernel.org/r/20251201194510.1121221-7-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

migration/multifd.c

@@ -1068,6 +1068,7 @@ static void multifd_recv_terminate_threads(Error *err)
     if (err) {
         MigrationState *s = migrate_get_current();
         migrate_set_error(s, err);
+        error_free(err);
         if (s->state == MIGRATION_STATUS_SETUP ||
             s->state == MIGRATION_STATUS_ACTIVE) {
             migrate_set_state(&s->state, s->state,
@@ -1434,7 +1435,6 @@ static void *multifd_recv_thread(void *opaque)
 
     if (local_err) {
         multifd_recv_terminate_threads(local_err);
-        error_free(local_err);
     }
 
     rcu_unregister_thread();
@@ -1535,7 +1535,7 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
     if (use_packets) {
         id = multifd_recv_initial_packet(ioc, &local_err);
         if (id < 0) {
-            multifd_recv_terminate_threads(local_err);
+            multifd_recv_terminate_threads(error_copy(local_err));
             error_propagate_prepend(errp, local_err,
                                     "failed to receive packet"
                                     " via multifd channel %d: ",
@@ -1551,7 +1551,7 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
     if (p->c != NULL) {
         error_setg(&local_err, "multifd: received id '%d' already setup'",
                    id);
-        multifd_recv_terminate_threads(local_err);
+        multifd_recv_terminate_threads(error_copy(local_err));
         error_propagate(errp, local_err);
         return;
     }