[Desktop Mode] GNOME Boxes hanging when VM plays sound

[pnaf]

Your system information

• Steam client version: 1660688177
• SteamOS version: 3.3.1
• SteamOS build: 20220817.1
• GNOME Boxes (Flatpak) version: 42.3-17184268
• Opted into Steam client beta?: No
• Opted into SteamOS beta?: No
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

In Desktop Mode, the GNOME Boxes Flatpak app hangs shortly after a booted VM plays sound for the first time.

This issue usually occurs if the VM is running a distro that installs or uses PulseAudio as the sound server. From what I've seen, GNOME Boxes VMs running distros that use PipeWire instead of PulseAudio (such as Ubuntu 22.10, Fedora 36, and GNOME OS Nightly) are much less likely to trigger this issue.

Here are some examples of VM live images with which I can trigger the issue virtually all of the time:

• Debian: debian-live-11.5.0-amd64-kde.iso
• Manjaro: manjaro-gnome-21.3.7-220816-linux515.iso
• PureOS: pureos-10~devel-gnome-live-20220602_amd64.iso

This issue also seems to be specific to SteamOS on the Steam Deck; if I use the Boot Manager to boot to a different distro (such as winesapOS, which is itself based on SteamOS 3), I can't seem to trigger this issue there.

Steps for reproducing this issue:

1. In Desktop Mode, open the "Boxes" application.
2. Click the "+" button in the top left corner.
3. Click "Create virtual machine from file", then open a live image.
4. Create a new VM using the default properties. Wait for the live image to boot.
5. Once the live image has booted, try playing a sound. Depending on the distro, you could do this by changing the volume (which might play a sound every time the volume is changed) or playing any sound file (such as any of those found in /usr/share/sounds).
6. The sound doesn't play, and the entire Boxes app will hang after a few seconds.

Steps for working around this issue:

1. While Boxes is unresponsive, try to close it by right-clicking its icon on the Plasma taskbar, then clicking "Close". Normally, this should instantly close Boxes, but since it's hanging, it may take a minute or so to actually close.
2. Open the "Boxes" application. If Boxes fails to start, try the following steps before trying to open it again:
   • Open the "System Monitor" application.
   • In the left sidebar, click "Processes".
   • End the gnome-boxes process.
3. Return to your VM and try playing a sound again. All sounds should be working now.