kworker processes with very high CPU usage.

[chicharras]

I am experiencing a nasty problem with my work laptop: Lenovo T61 -
Ubuntu 11.04 installed.

With a fresh reboot and only running System Monitor I see one of my
CPUs fluctuate from 5% utilization to 100% every 12 or so seconds.
The other CPU fluctuates with the same frequency from 5% to 40%.
Nothing other than System Monitor is running.
Once I start the applications I work with, I experience very annoying
periodic delays in response time.
The top command shows some "kworker" processes that are taking all the
CPU. Here is a snapshot:

top - 09:08:58 up 5 min,  2 users,  load average: 0.86, 0.85, 0.41
Tasks: 151 total,   3 running, 147 sleeping,   0 stopped,   1 zombie
Cpu(s): 14.3%us, 34.7%sy,  0.0%ni, 51.1%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   3070088k total,   659492k used,  2410596k free,    62932k buffers
Swap:  3927888k total,        0k used,  3927888k free,   338940k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
   10 root      20   0     0    0    0 S   66  0.0   1:21.81 kworker/0:1
 1587 cesar     20   0 91680  19m  15m R   22  0.6   0:41.93 gnome-system-mo
  878 root      20   0 61672  18m 8724 R    7  0.6   0:18.54 Xorg
 1361 cesar     20   0  259m  46m  20m S    2  1.6   0:07.25 compiz
   25 root      20   0     0    0    0 S    0  0.0   0:00.27 kworker/1:1

I always install all the updates offered by Update Manager. The last
entries in /var/log/dpkg.log show that yesterday I installed some PAM
stuff as shown by:

2011-10-25 07:47:32 upgrade libpam0g 1.1.2-2ubuntu8.3 1.1.2-2ubuntu8.4
etc...

and a new kernel:
2011-10-25 07:47:51 install linux-image-2.6.38-12-generic <none> 2.6.38-12.51
etc...

The problem exists even if I boot with my previous kernels. I have tested:
2.6.38-12-generic
2.6.38-11-generic
2.6.38-10-generic
2.6.38-8-generic

So, could this problem be caused by the updates to the PAM stuff?
Can anyone please indicate if and how I could roll back these updates?
Any pointers will be appreciated.

Note: I googled quite a while and found many hits but none are
conclusive to me. Like the following bug with kernel 2.6.37:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/717919


Thanks