Re: [pve-devel] [PATCH] systemd: disconnect signals

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Mon, Mar 03, 2025 at 03:42:53PM +0100, Maximiliano Sandoval wrote:
> Dbus has a limit of 512 connections by default and signals should be
> disconnected as soon as they are not needed anymore.
> 
> This should alleviate https://bugzilla.proxmox.com/show_bug.cgi?id=5876.
> 
> Signed-off-by: Maximiliano Sandoval <m.sandoval@proxmox.com>
> ---
>  src/PVE/Systemd.pm | 34 ++++++++++++++++++++++++++++------
>  1 file changed, 28 insertions(+), 6 deletions(-)
> 
> diff --git a/src/PVE/Systemd.pm b/src/PVE/Systemd.pm
> index 07c912e3..1d7772d9 100644
> --- a/src/PVE/Systemd.pm
> +++ b/src/PVE/Systemd.pm
> @@ -44,6 +44,7 @@ sub unescape_unit {
>  # main loop is being used as we need to wait signals.
>  sub systemd_call($;$) {
>      my ($code, $timeout) = @_;
> +    my $signal_info;
>  
>      my $bus = Net::DBus->system();
>      my $reactor = Net::DBus::Reactor->main();
> @@ -64,13 +65,22 @@ sub systemd_call($;$) {
>  	    $timer = undef;
>  	}
>  
> +	if (defined($signal_info)) {
> +	    if (my $signal_name = $signal_info->{name}) {
> +		if (my $signal_handle = $signal_info->{handle}) {

I think it's enough to require the info to either be valid or undef,
therefore the first `if` should suffice.

> +		    $if->disconnect_from_signal($signal_name, $signal_handle);
> +		}
> +	    }
> +	    $signal_info = undef;
> +	}
> +
>  	if (defined($reactor)) {
>  	    $reactor->shutdown();
>  	    $reactor = undef;
>  	}
>      };
>  
> -    my $result = $code->($if, $reactor, $finish_callback);
> +    (my $result, $signal_info) = $code->($if, $reactor, $finish_callback);
>      # Are we done immediately?
>      return $result if defined $result;
>  
> @@ -124,7 +134,8 @@ sub enter_systemd_scope {
>  
>  	my $job;
>  
> -	$if->connect_to_signal('JobRemoved', sub {
> +	my $signal_name = 'JobRemoved';
> +	my $signal_handle = $if->connect_to_signal($signal_name, sub {
>  	    my ($id, $removed_job, $signaled_unit, $result) = @_;
>  	    return if $signaled_unit ne $unit || $removed_job ne $job;
>  	    if ($result ne 'done') {
> @@ -139,7 +150,12 @@ sub enter_systemd_scope {
>  
>  	$job = $if->StartTransientUnit($unit, 'fail', $properties, []);
>  
> -	return undef;
> +	my $signal_info = {
> +	    name => $signal_name,
> +	    handle => $signal_handle,
> +	};
> +
> +	return (undef, $signal_info);
>      }, $timeout);
>  }
>  
> @@ -152,18 +168,24 @@ sub wait_for_unit_removed($;$) {
>  	my $unit_obj = eval { $if->GetUnit($unit) };
>  	return 1 if !$unit_obj;
>  
> -	$if->connect_to_signal('UnitRemoved', sub {
> +	my $signal_name = 'UnitRemoved';
> +	my $signal_handle = $if->connect_to_signal($signal_name, sub {
>  	    my ($id, $removed_unit) = @_;
>  	    $finish_cb->(1) if $removed_unit eq $unit_obj;
>  	});
>  
> +	my $signal_info = {
> +	    name => $signal_name,
> +	    handle => $signal_handle,
> +	};
> +
>  	# Deal with what we lost between GetUnit() and connecting to UnitRemoved:
>  	my $unit_obj_new = eval { $if->GetUnit($unit) };
>  	if (!$unit_obj_new) {
> -	    return 1;
> +	    return (1, $signal_info);
>  	}
>  
> -	return undef;
> +	return (undef, $signal_info);
>      }, $timeout);
>  }
>  
> -- 
> 2.39.5


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