Compiz desktop freeze VirtualBox resize

[Guy Rouillier]

Ubuntu Mate 21.10, running in a VirtualBox VM. With window manager set to Compiz (Advanced GPU accelerated desktop effects), resizing the VM window causes the desktop to freeze. I cannot move icons on the desktop, and the task bar does not react to mouse clicks. I cannot get to the system menu. If I start the VM but never resize the VM window, Compiz works fine.

If I switch the window manager to Marco (Adaptive compositor), everything works fine. I can resize the VM window without any apparent ill effects.

I've tried going back a couple of kernel releases, and also rolling back to previous VirtualBox releases. Nothing seems to help. I really can't remember if resizing the VM window ever worked with the Compiz window manager. I don't resize the VM window all that often.

I also have a Linux Mint 20.3 VM, and selecting Compiz window manager allows me to resize the VM window without freezing. The version of VirtualBox is obviously the same; however, this latest version of Linux Mint Mate uses a much older kernel: 5.4.0-97.

[Guy Rouillier (guy-rouillier)]

I installed a prebuilt Ubuntu Mate 21.10 image from OSBoxes.org, which starts with kernel 5.13.0-19. Then I tried 2 upgrade paths to the current kernel 5.13.0-28: (1) starting with the Marco window manager, upgrading, then switching to Compiz, and (2) starting with Compiz and upgrading. With both approaches, the resulting Compiz environment does *not* freeze the desktop when I resize the VM window.

I matched the VirtualBox configuration options for this OSBoxes VM to my own Ubuntu Mate 21.10 VM (where I'm experiencing this issue.) The settings seem to be the same. However, comparing CompizConfig Settings Manager between the two, they are very different, even though they are the same version: 0.9.14.1. For example, in my VM, the Effects category contains 18 options, while in the OSBoxes VM, that same category only has 3 options.

I noticed in the CompizConfig Settings Manager, on the Preferences page, an option under Profile to "Reset to defaults". Before trying drastic steps like uninstalling and reinstalling Compiz, I decided to try this Reset. While my VM continues to show many more options than the OSBoxes, VM, resizing the VM window no longer freezes the desktop. So apparently some combination of these options was causing the problem. I had never using this CompizConfig Settings Manager, so apparently the settings got changed by other means.

This problem is no longer affecting me, so this report can be closed for my purposes. If anyone would like, I can try to change some of the CompizConfig Settings Manager options to see if I can get the problem to recur.