Misc. kernel preemption-related bits.  Specifically,

 - update to Documentation/preempt-locking.txt (me)

 - preempt-safe arch/i386/kernel/ioport.c :: sys_ioperm()
   (George Anzinger)

 - remove "kernel_lock()" cruft in include/linux/smp.h
   (Andrew Morton)

 - we have a debug check in preempt_schedule that, even
   on detecting a schedule with irqs disabled, still goes
   ahead and reschedules.  We should return. (me)

 - preempt-safe net/core/dev.c :: netif_rx() (George Anzinger)