Linux WiFi: operation not possible due to RF-kill

Some people have been experiencing WiFi problems with Ubuntu 10.10 since an update that happend just before Christmas 2010. The problem seems to be a bug in a kernel module, which prevents the
rfkill's soft and hard block from syncing correctly.

In practice that means you can press your laptop's WiFi button as often as you want, it doesn't change anything. Your wireless adapter will always appear as disabled. If you try to start the wireless interface manually you get the following error message:

sk@ubuntu:~# sudo ifconfig wlan0 up

SIOCSIFFLAGS: Operation not possible due to RF-kill
If you do a rfkill list all you should get an output similar to this:

sk@ubuntu:~$ sudo rfkill list all

0: hp-wifi: Wireless LAN

Soft blocked: yes

Hard blocked: no

1: phy0: Wireless LAN

Soft blocked: yes

Hard blocked: no
Depending on the state of your WiFi button the Hard blocked will either be
yes or no. Press the WiFi button and run
rfkill list all again to make sure the value for
Hard blocked changes.

The actual problem is, that the Soft blocked value is always set to
yes, because for some reason the syncing between the hardware block and the software block doesn't work as supposed. To override this behavior, you can just run
rfkill unblock wifi and it should work again. Double check by entering
rfkill list all again and make sure it looks like this, with all values set to
no:

sk@ubuntu:~$ sudo rfkill list all

0: hp-wifi: Wireless LAN

Soft blocked: no

Hard blocked: no

1: phy0: Wireless LAN

Soft blocked: no

Hard blocked: no
If you then run ifconfig wlan0 up (or enable the wireless via your desktop's network manager) you should be able to connect to a wireless network again without any further issues.

The configuration, which I've been using:

Compaq Presario CQ60
Atheros AR5001 Wireless Network Adapter
Ubuntu 10.10

I also read, that some people could fix it, by turning off the WiFi button during the boot process and then switch it on again, once the system is up and running. It seems that the system expects the hard block to be set to off. This is still a bug, but it
could explain why then the soft block didn't sync with the hard block any more.