user switching from screen lock freezes system

[Zaris]

There are tow or more users logged in system but last has locked the screen.
Move mouse. Authentication dialogue appears.
Click Switch User.
Lightdm login screen appears.
Select user (allready logged in but with locked session) and type password and enter.
Screen goes black (or somtimes a gray bar appears at bottom of screen). Fan gets noisy so some process probably went crazy. Only way out is reset button.
I can however switch user by ctr-alt Fn (if I know which tty my session is)

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: lightdm 1.0.1-0ubuntu6
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic-pae 3.0.4
Uname: Linux 3.0.0-12-generic-pae i686
NonfreeKernelModules: fglrx
ApportVersion: 1.23-0ubuntu4
Architecture: i386
Date: Sat Nov 5 17:08:00 2011
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111012)
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, no user)
 LANG=fi_FI.utf8
 SHELL=/bin/bash
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[udippel (udippel)]

Check with bug 886496, filed by me. Does it have anything to do with it? It looks like possibly related.
Take out the 'Energy Saving Part' from your system.

[Launchpad Janitor (janitor)]

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

[Roman Bazalevsky (rvbglas)]

Same problem with fglrx, but works fine with opensource radeon driver.

[Zaris (zaris)]

Some more testing:
No (this) problem with opensource radeon driver.
Problem exists also with gdm (finally got it working when removed automatic login, otherwise hang in checking battery -in desktop-).

So it's not lightdm (only) and seems to be related to fglrx. (Also tried with latest version from AMD with same result.)

Currently workaround seems to be ctrl-alt Fn (but what Fn?) or logging out when leaving.

Next I will try to change gnome screensaver to xscreensaver (but I don't expect much...)

[Zaris (zaris)]

OK, it's the same with xcreensaver. Only with opensource driver I can switch to locked session from dm. With fglrx the system freezes.

It might be that dm is trying to create a new session even when there is existing one but locked and that's why it hangs?

[Roman Bazalevsky (rvbglas)]

I still can log in via ssh, and I see Xorg consuming 100% CPU and immune to kill -9 (what the damn?!!!). sudo reboot still works. so hard reset is not really the only way.

[Zaris (zaris)]

After last updates system freezes when user switching also with os-radeon :-(

[Farid Joubbi (farid)]

I have the same problem.

This old bug seems to be the same:
https://bugs.launchpad.net/ubuntu/+source/linux-restricted-modules-2.6.20/+bug/112518

A thread discussing the problem:
http://ubuntuforums.org/showthread.php?t=1890581

Instead of using the reset button, I do this:
Alt+PrntScr+r, Alt+PrntScr+s, Alt+PrntScr+e, Alt+PrntScr+i, Alt+PrntScr+n, Alt+PrntScr+u, Alt+PrntScr+b
These key-presses will reboot the system safely.

[Colin (colin-)]

For me it seems like it's a lot more likely to happen when switching from a user with Terminal open. Particularly if I'm using sudo.