worker: disconnect dbus from NameOwnerChanged signal (POO #183833)

This avoids us piling up signals we never handle and eventually
exceeding a dbus quota limit and causing all subsequent tap jobs
to fail.

New Net::DBus instances are automatically connected to this signal
on creation, you cannot change this. If the instance is kept
around but nothing iterates the dbus event loop once in a while,
that signal will just keep piling up messages indefinitely. We
encountered this once before in os-autoinst and "solved" it by not
persisting the dbus connection, but in this case it doesn't seem a
good idea to re-initialize that connection every time we want to
check on the status of a tap worker. So instead let's disconnect
it from the signal.

The 1 here is a bit magical. The Net::DBus connect_to_signal
method issues signal numbers on a first-come, first-served basis,
starting at 1 (0 is never used), and returns the number it
issued. When Net::DBus _new calls it, though, it doesn't record
the return value. So we have to know/guess that this will always
be the first signal connected.

Related ticket: https://progress.opensuse.org/issues/183833

Signed-off-by: Adam Williamson <[email protected]>

Author: AdamWill

lib/OpenQA/Worker.pm

@@ -611,8 +611,12 @@ sub is_qemu_running ($self) {
 sub is_ovs_dbus_service_running ($self) {
     try { defined &Net::DBus::system or require Net::DBus }
     catch ($e) { return 0 }
-    my $bus = ($self->{_system_dbus} //= Net::DBus->system(nomainloop => 1));
-    try { return defined $bus->get_service('org.opensuse.os_autoinst.switch') }
+    unless (defined $self->{_system_dbus}) {
+        $self->{_system_dbus} = Net::DBus->system(nomainloop => 1);
+        # this avoids piling up signals we never do anything with - POO #183833
+        $self->{_system_dbus}->get_bus_object->disconnect_from_signal('NameOwnerChanged', 1);
+    }
+    try { return defined $self->{_system_dbus}->get_service('org.opensuse.os_autoinst.switch') }
     catch ($e) { return 0 }
 }
 

t/24-worker-overall.t

@@ -80,11 +80,17 @@ my $guard = scope_guard sub { chdir $FindBin::Bin };
     use Mojo::Base -base;
     has availability_error => 'Cache service info error: Connection refused';
 }
+{
+    package Test::FakeDBusObject;
+    use Mojo::Base -base, -signatures;
+    sub disconnect_from_signal ($self, $signal, $id) {}
+}
 {
     package Test::FakeDBus;    # uncoverable statement count:2
     use Mojo::Base -base, -signatures;
     has mock_service_value => 1;
     sub get_service ($self, $service_name) { $self->mock_service_value }
+    sub get_bus_object ($self) { Test::FakeDBusObject->new }
 }
 
 my $dbus_mock = Test::MockModule->new('Net::DBus', no_auto => 1);