Switch user does not work

[Robert Sander]

When trying to switch to another user lightdm tries to start a new xserver (which crashes) and then the system stays on tty8.

Manually switching back to tty7 by pressing ALT-F7 works.

But it is not possible to start a new user session.

/var/log/Xorg.1.log contains:

[ 8756.298] (II) fglrx(0): Kernel Module Version Information:
[ 8756.298] (II) fglrx(0): Name: fglrx
[ 8756.298] (II) fglrx(0): Version: 8.91.4
[ 8756.298] (II) fglrx(0): Date: Oct 25 2011
[ 8756.298] (II) fglrx(0): Desc: ATI FireGL DRM kernel module
[ 8756.298] (II) fglrx(0): Kernel Module version matches driver.
[ 8756.299] (II) fglrx(0): Kernel Module Build Time Information:
[ 8756.299] (II) fglrx(0): Build-Kernel UTS_RELEASE: 3.0.0-16-generic
[ 8756.299] (II) fglrx(0): Build-Kernel MODVERSIONS: yes
[ 8756.299] (II) fglrx(0): Build-Kernel __SMP__: yes
[ 8756.299] (II) fglrx(0): Build-Kernel PAGE_SIZE: 0x1000
[ 8756.299] (II) fglrx(0): [uki] register handle = 0x00004000
[ 8756.299] (II) fglrx(0): FIREGL Board Found
[ 8756.307] (EE) fglrx(0): Not enough video memory to allocate shared Z/stencil buffer.
[ 8756.314] (II) fglrx(0): Shutdown CMMQS
[ 8756.317] (II) fglrx(0): [uki] removed 1 reserved context for kernel
[ 8756.317] (II) fglrx(0): [uki] unmapping 8192 bytes of SAREA 0xee000 at 0x7f7a68290000

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: fglrx-updates 2:8.911-0ubuntu0.1
ProcVersionSignature: Ubuntu 3.0.0-16.28-generic 3.0.17
Uname: Linux 3.0.0-16-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 1.23-0ubuntu4
Architecture: amd64
Date: Thu Feb 23 22:59:26 2012
ProcEnviron:
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: fglrx-installer-updates
UpgradeStatus: Upgraded to oneiric on 2011-10-23 (123 days ago)

[Robert Sander (gurubert)]

This also happens on the same hardware running natty:

[347395.593] (II) fglrx(0): Kernel Module Version Information:
[347395.593] (II) fglrx(0): Name: fglrx
[347395.593] (II) fglrx(0): Version: 8.85.6
[347395.593] (II) fglrx(0): Date: Apr 19 2011
[347395.593] (II) fglrx(0): Desc: ATI FireGL DRM kernel module
[347395.593] (II) fglrx(0): Kernel Module version matches driver.
[347395.593] (II) fglrx(0): Kernel Module Build Time Information:
[347395.593] (II) fglrx(0): Build-Kernel UTS_RELEASE: 2.6.38-13-generic
[347395.593] (II) fglrx(0): Build-Kernel MODVERSIONS: yes
[347395.593] (II) fglrx(0): Build-Kernel __SMP__: yes
[347395.593] (II) fglrx(0): Build-Kernel PAGE_SIZE: 0x1000
[347395.593] (II) fglrx(0): [uki] register handle = 0x00004000
[347395.593] (II) fglrx(0): FIREGL Board Found
[347395.597] (EE) fglrx(0): Not enough video memory to allocate back buffer.
[347395.601] (II) fglrx(0): Shutdown CMMQS
[347395.603] (II) fglrx(0): [uki] removed 1 reserved context for kernel
[347395.603] (II) fglrx(0): [uki] unmapping 8192 bytes of SAREA 0x3b82f000 at 0x7f529f0f6000

[Robert Sander (gurubert)]

According to http://forums.gentoo.org/viewtopic-t-888290-start-0.html this could be a conflict with the framebuffer device.

I will try and compile a kernel without builtin fbdev and see if this solves this issue.

[Felix Kuehling (felix-kuehling)]

I think the problem is that you're simply running out of video memory. Each user session runs in its own Xserver. Each Xserver needs video memory for various render and display buffers. A number of factors influence video memory usage:

* number and size of attached monitors
* virtual desktop size
* driver features requiring additional video memory per monitor:
  - monitor rotation
  - tear-free desktop
  - OpenGL overlay
  - stereo 3D
* 3D OpenGL applications
* composite manager
* 2D applications

If the system has been running for a while, video memory fragmentation can also prevent successful allocation of the required buffers even if the raw amount of free memory would be sufficient.

[Robert Sander (gurubert)]

I cannot believe that this is really a memory issue.

Yesterday I exchanged the hardware from a single monitor with 128MB nVidia graphics card to a dual monitor setup with a 256MB ATI Technologies Inc RV730 [FirePro V5700].

The user switching was working flawlessly with the nVidia proprietary driver, but now with AMD it does not work any more.

[Robert Sander (gurubert)]

I removed the fglrx package and configured X to use the radeon driver with the two monitors.

With the radeon X11 driver I am able to switch users.

I still think this is an fglrx issue.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[ari e (aesop)]

I am using a single-monitor 1280x1024 setup with a 256M FireGL V3700, and a similar issue is exhibited (differing only in log output). I have successfully used a dual-monitor setup with this card where _both_ monitors had higher resolution than this one; I agree that this is not likely to be caused by a lack of sufficient memory to start an X server.

The issue remains when no compositing manager is running, and on a system that has been booted recently.

Logs:

(==) Log file: "/var/log/Xorg.1.log", Time: Tue Mar 20 05:52:50 2012
(==) Using config file: "/etc/X11/xorg.conf"
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
(EE) fglrx(0): Not enough video memory to allocate back buffer.

Fatal server error:
AddScreen/ScreenInit failed for driver 0