Kernel BUG at kernel/timer.c:681 and broken ext4

I just ran into a mysterious issue with a Virtualbox virtual machine running linux kernel 2.6.37-rc1 (although this might not be kernel specific). After a power outage, reboot always ended with a kernel panic with the following message (among a rather long screen dump):

Clocksource tsc unstable (delta = 784015673 ns)

---[ end trace a732f57055898f20 ]---

Switching to clocksource acpi_pm

Kernel panic - not syncing: Attempted to kill init!

[...]

kernel BUG at kernel/timer.c:681!

invalid opcode: 0000 [#1]

last sysfs file:

CPU0

Modules linked in:

[...]

First, I found many forum posts stating that tsc clocksource has to be replaced with acpi_pm (or something else) already in GRUB, but this didn't help. Then I figured that in recovery mode, having fsck to repair the root filesystem, puts it back to normal. So: even though it does not seem to be related, a broken filesystem can cause the kernel panic above!

Invisible mouse pointer in Debian Squeeze (Debian 6) - Resolved!

Previously, I wrote about a rather serious bug in Debian 6, which prevented the mouse pointer to appear in any X session. However, upon a sleep or hibernation and recovery the pointer came back. As now I wanted to use the laptop which was affected by this issue, I had to look into the solution as well, as there is nothing on how to resolve this on the bugtracker page. Luckily enough I found a rather good point on another page. The main point is that according to the bugtracker, the Intel video driver is already fixed in the proposed update 2.6.32-32 but it cannot be moved to the mainline. For x86, however, it works just fine so that we can install it. To do so, add two lines to the end of the /etc/apt/sources.list file:

deb http://ftp.us.debian.org/debian squeeze-proposed-updates main contrib non-free

deb-src http://ftp.us.debian.org/debian squeeze-proposed-updates main contrib non-free

The domain name can be replaced to match the earlier entries in sources.list. Then as root, simply issue:

root@gxa01:~# apt-get update

root@gxa01:~# apt-get upgrade

The upgradable packages will be shown and most likely some additional packages such as libc, and apt itself will be upgraded. Then reboot, and enjoy your system with a mouse :)

Invisible mouse pointer in Debian Squeeze (Debian 6)

I just updated Debian 6 on my computer and have no mouse pointer since then. Apparently the latest kernel update to 2.6.32.5 reintroduces a bug that has already been resolved. Many Intel VGA chips are affected, mostly on Centrino and Core platform including the i855GM that my laptop have.

root@gxa01:~# uname -a
Linux gxa01 2.6.32-5-686 #1 SMP Tue Mar 8 21:36:00 UTC 2011 i686 GNU/Linux

root@gxa01:~# lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation 82852/855GM Integrated Graphics Device (rev 02)

Temporary resolution is to put the system into suspend/hibernation after which the pointer reappears. One can also upgrade/downgrade the system, as other kernel versions are reported to work. Anyway the best would be the Debian guys to fix the mainline kernel ;)

Update: Solution is here.