preempt cause series of oopses in 2.5.22 and 2.5.22-dj1

[Helge Hafting <helgehaf@aitel.hist.no>]

Booting a UP kernel compiled with preempt
(2.5.22, 2.5.22-dj1 and several earlier ones)
results in a series of oopses when running boot scripts, typically
when xdm is about to start.  I can start up single-
user and run X though, I haven't figured out exactly where
it goes wrong.

The oopses scrolling by all starts with
init[454] exited with preempt-count xx
where xx increase by 3 for each oops.  
The call trace is longer each time.
The scrolling stops when this counter reach 63 or 66, 
probably running out of some resource such as kernel stack.

I haven't written down the last oops assuming it is the first
one that is interesting, but I can reproduce and write
down details if someone thinks it makes a difference.

The kernels are compiled with preempt, vesafb, devfs.
Recompiling without preempt gives me a kernel
that works fine.

This preempt problem seems to have existed at least
since 2.5.12-dj1, it took some time before I figured
out it was a preempt problem.

Helge Hafting