Verification done for resolute: xorg-server 2:21.1.22-1ubuntu1.3 from
resolute-proposed fixes the crash.

Test system:
- HP Pavilion x360 14-dh1xxx (Intel CometLake-U UHD, modesetting), Secure Boot 
enabled
- Ubuntu Cinnamon 26.04.1 live session (X11, real Xorg via LightDM), kernel 
7.0.0-30-generic
- DisplayLink USB3.0 UHD DisplayPort Adapter (17e9:4301) with a monitor attached
- displaylink-driver 6.4.0-22, evdi from 
linux-main-modules-evdi-7.0.0-30-generic 7.0.0-30.30 (signed by Canonical), 
libevdi1 1.14.15+dfsg-0ubuntu1
- evdi initial_device_count=0 (the module default), so DisplayLinkManager 
creates the evdi device after X is running

Steps, run identically on each version:
1. Stop lightdm and displaylink-driver, reload evdi so no evdi device exists.
2. Start lightdm (X comes up with no evdi GPU), then start displaylink-driver. 
Xorg.0.log shows the runtime add: "config/udev: Adding drm device 
(/dev/dri/card0)", "modeset(G0): using drv /dev/dri/card0".
3. Restart lightdm, which tears the X server down with the hotplugged GPU 
screen still present.

Before, 2:21.1.22-1ubuntu1.2 (resolute-updates): the teardown crashes,
as in the bug description:

    (EE) Segmentation fault at address 0x0
    (EE) Caught signal 11 (Segmentation fault). Server aborting
    (EE) Server terminated with error (1). Closing log file.

and systemd-coredump records an Xorg core (SIGABRT from the signal
handler).

After, 2:21.1.22-1ubuntu1.3 (resolute-proposed): same steps, run twice.
Each time the runtime add appears in the log, the GPU screen is torn
down ("UnloadModule: modesetting") and the server exits cleanly ("Server
terminated successfully (0)"), with no core dumps. The DisplayLink
monitor is active under 1.3 (DVI-I-1-1 at 1280x1440 in xrandr), so the
adapter still works normally.

The udev NULL-subsystem fix in the same upload is a teardown race that
can't be triggered on demand (see the test plan); it did not fire in
these runs, and nothing regressed.

Changing the tag to verification-done-resolute.


** Tags removed: verification-needed-resolute
** Tags added: verification-done-resolute

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https://bugs.launchpad.net/bugs/2160643

Title:
  xorg-server SIGSEGV on runtime GPU-screen (DisplayLink/evdi) hotplug
  -- NULL SetDGAMode and NULL udev subsystem

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