Hi,

this one crapped out on me, while having heavy disk activity. (updating 
  gentoo portage tree - rebuilding metadata of it). Unfortunately I 
couldn't save the oops, as I had no hd access anymore and X would freeze 
a little later...(and I don't want to risk my data a second time...)

I think it had to do with preempt, or even preempt big kernel lock, as I 
could read something about it. I applied your patch to 2.6.10_rc3-ck1. I 
attached my config, if you want to try yourself with that kernel. cfq2 
runs w/o probs.

Cheers,

Prakash