linux user mode cpu loop driver 304.54 GTX 295

Do the Unix nVidia drivers operate in user mode?

Just in case this might be useful for others…
I have been seeing weird behaviour from an image compiled with nvcc CUDA 5.0
with GTX 295 driver 304.54 which is not seen in a similar linux server
also with driver 304.54 but a c2050
In the first it spent a huge amount of time in user mode and eventually hit
a cpulimit and the image was terminated. Oddly the wall clock CUDA GPU kernel times were not
affected. Something elsewhere appears to have been looping. This also happened
when loging on via the console without X-11 windows running and affected both gtx295 devices.
After reboot the server/GTX 295 (with the same image) is ok.