Hello,

This patch solves a coding problem that was noticed during hotplug 
driver testing on SGI systems. 

When a hotpluggable PCI device is introduced to the system, it is linked 
to a sn_irq_info struct.  These sn_irq_info tructs are linked together 
via a unprotected unidirectional list, which implies FIFO list 
behaviour.  If a PCI device was taken out of service the sn_irq_info 
struct must be removed.

Due to the FIFO nature of the list, the element remove function became 
cumbersome to code. Since the list was unprotected by locks a race was 
quickly noticed where sn_irq_info structs were accessed as they were 
being removed.

The fix is to implement a list using the standard list.h structs and to 
lock using an RCU lock implementation (the list can be accessed in an 
interrupt context).

The attached patch is against latest 2.6 bk pull.

P.