global_irq_count vs global_irq_lock

Hello,

This is probably a kernel newbie question so my apologies in advance.

I have a design/implementation question.

global_irq_count is defined as atomic_t whereas globall_irq_lock is defined as unsigned volatiile int.
Is this by design? or by chance?

Why would you be concerned about reading global_irq_count atomically and not global_irq_count as it is done is several
functions in linux/arch/i386/irq.c in kernel 2.2.18.

If it is by design, what am I missing.

Please cc me on your respone as I am not on the list.

Take care!