Possible race in x86 global_irq_lock handling.

[TeJun Huh]

 I've been reading x86 interrupt handling code for a couple of days
and encountered something which I believe is a race condition.  It's
betweewn include/asm-i386/hardirq.h:irq_enter() and
arch/i386/kernel/irq.c:get_irqlock().  Lockless synchronization using
memory ordering seems to be used to achieve global irq locking.

 in get_irqlock()

static inline void irq_enter(int cpu, int irq)
{
	++local_irq_count(cpu);

	while (test_bit(0,&global_irq_lock)) {
		cpu_relax();
	}
}

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