Linux guest machines crash frequently

[raccoon]

I am running VirtualBox 6.1.34 on a Debian 11 (bullseye) host. I am trying to run an existing Debian 11 guest with Xfce. There was no problem with the Debian guest until (I think) the update to 6.1.34. The virtual machine now inevitably crashes after a few minutes, either logging me out (and so closing all the programs that were running in the guest) or showing a blank screen with a blinking cursor.

I am also trying to install Fedora 35 with Gnome and Debian 11 with Gnome as guests. Both show the same behaviour, logging out or crashing after a few minutes. In the case of Fedora, this happens in the live session and so it is impossible to install. In the case of Debian, I completed the installation with the text mode installer, but the Gnome session logs out and crashes just as with the other virtual machines.

Around the time that Fedora crashed, I saw this in VBox.log:

00:04:24.062615 VMMDev: Guest Log: A fatal guest X Window error occurred.  This may just mean that the Window system was shut down while the client was still runnA fatal guest X Window error occurred.  This may just mean that the Window system was shut down while the client was still runnA fatal guest X Window error occurred.  This may just mean that the Window system was shut down while the client was still runnTerminating ...
00:04:24.067113 VMMDev: Guest Log: Terminating HGCM thread ...
00:04:24.159654 VMMDev: Guest Log: Terminating X11 thread ...
00:04:24.366621 VMMDev: Guest Log: Error waiting for X11 thread to terminate: VERR_TIMEOUT
00:04:24.367742 VMMDev: Guest Log: Terminating threads done

However, I don't see any similar entries in the logs for the Debian machines.

The problem affects all my guest machines, all of which are Linux. It definitely did not affect these or other previous Linux guest machines until very recently. Therefore, I can only assume it is a problem with VirtualBox.

[galitsyn]

Hi raccoon,

It smells it could be a duplicate of #20914. Could you please try one of the "Latest 6.1.x test builds" from https://www.virtualbox.org/wiki/Testbuilds. Any revision starting from r151864 should have the fix.

[raccoon]

I installed the 6.1.35 test build and it fixed the problem for all guests. For reference, the host machine is running kernel 5.10.0 and the guest machines are running 5.10.0 and 5.17.5, so if it is the same issue, it's not specific to kernel 5.18.

Thanks for your help!

[galitsyn]

Thank you for the feedback. Closing as a duplicate of #20914.