X Server crashes on NVIDIA systems when DisplayLink device present during login or logout

Symptoms


In systems running Ubuntu 18.04 with NVIDIA graphics users may experience X Server crashes when DisplayLink device is connected before the X Server starts. This applies to systems using an NVIDIA-only GPU setup, or a combination of integrated Intel GPU and a discrete NVIDIA GPU.

On affected platforms, some or all of the following issues can be observed:

  • System crashes during logout with DisplayLink device plugged in.
  • It is impossible to log in with DisplayLink device plugged in.

Workaround: Switch XServer DDX driver to modesetting

To workaround that issue, it is necessary to force using modesetting driver globally, for all GPUs.

To do this, as a root user create a file 21-displaylink.conf under:

/usr/share/X11/xorg.conf.d/

with the following content for Ubuntu: 

Section "Device"
  Identifier "DisplayLink"

  Driver "modesetting"
  Option "PageFlip" "false"
EndSection 

A reboot is required for the setting to be effective.

Technical details

The root cause for the problem is X.org window system choosing incorrect DDX driver for DisplayLink devices, and attempting to use 'nouveau’ instead of ‘modesetting’.

The situation is happening only when X.org window system starts, and it does not happen when you connect DisplayLink devices after logging in - correct driver is selected for the device in such cases.

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