[Pkg-raspi-maintainers] Lightdm and Xfce4 results in blank screen

[Arjen Balfoort]

I'm using Michael Stapelberg's 2018-01-08 RPI3 preview image.

After a dist-upgrade I installed lightdm and xfce4:
apt-get install lightdm lightdm-gtk-greeter xfce4 xfce4.*plugin 
xfce4-terminal xfce4-taskmanager xfce4-screenshooter xfce4-clipman 
gtk3-engines-xfce xfce4-notes xfce4-notifyd xfce4-power-manager

After a reboot lightdm is correctly started but after login it hangs on 
a blank screen with a mouse pointer. I added these lines to config.txt 
as mentioned here: 
http://lists.alioth.debian.org/pipermail/pkg-raspi-maintainers/Week-of-Mon-20180108/000149.html
cma_lwm=16
cma_hwm=256
cma_offline_start=16

Unfortunately, that didn't make a difference.

journalctl shows these errors:
kernel: vc4-drm soc:gpu: failed to allocate buffer with size 8355840 
(multiple times)
at-spi-bus-launcher[1388]: XIO:  fatal IO error 11 (Resource temporarily 
unavailable) on X server ":0"
xfce4-notifyd[1405]: xfce4-notifyd: Fatal IO error 11 (Resource 
temporarily unavailable) on X server :0.
pulseaudio[1383]: XIO:  fatal IO error 11 (Resource temporarily 
unavailable) on X server ":0.0" (and a bunch of other pulseaudio errors)

The last 25 lines of /var/log/Xorg.0.log show:
[   108.955] (II) modeset(0): Modeline "1920x1080i"x0.0   74.25 1920 
2448 2492 2640  1080 1084 1094 1125 interlace +hsync +vsync (28.1 kHz e)
[   108.955] (II) modeset(0): Modeline "1440x576i"x0.0   27.00  1440 
1464 1590 1728  576 580 586 625 interlace -hsync -vsync (15.6 kHz e)
[   108.955] (II) modeset(0): Modeline "1920x1080"x0.0  148.50  1920 
2448 2492 2640  1080 1084 1089 1125 +hsync +vsync (56.2 kHz e)
[   112.773] (WW) glamor: Failed to allocate 1920x1080 FBO due to 
GL_OUT_OF_MEMORY.
[   112.774] (WW) glamor: Expect reduced performance.
[   112.872] (EE) glamor0: GL error: GL_OUT_OF_MEMORY in glBufferData
[   112.873] (EE) glamor0: GL error: GL_INVALID_OPERATION in 
glReadPixels(out of bounds PBO access)
[   112.873] (EE) glamor0: GL error: GL_INVALID_OPERATION in 
glMapBuffer(length = 0)
[   112.874] (EE)
[   112.874] (EE) Backtrace:
[   112.874] (EE) 0: /usr/lib/xorg/Xorg (xorg_backtrace+0x5c) 
[0xaaaabc08fd54]
[   112.874] (EE)
[   112.875] (EE) Segmentation fault at address 0x0
[   112.875] (EE)
Fatal server error:
[   112.875] (EE) Caught signal 11 (Segmentation fault). Server aborting
[   112.875] (EE)
[   112.875] (EE)
Please consult the The X.Org Foundation support
      at http://wiki.x.org
  for help.
[   112.876] (EE) Please also check the log file at 
"/var/log/Xorg.0.log" for additional information.
[   112.876] (EE)
[   112.876] (II) AIGLX: Suspending AIGLX clients for VT switch
[   112.997] (EE) Server terminated with error (1). Closing log file.

I've searched for two days but all to no avail.

Running startx manually results in the same errors.

Has anyone seen this before and knows what's missing?