Re: Possible race condition in i386 global_irq_lock handling.

[Manfred Spraul]

TeJun wrote:
> static inline void irq_enter(int cpu, int irq)
> {
> 	++local_irq_count(cpu);
>
> 	while (test_bit(0,&global_irq_lock)) {
> 		cpu_relax();
> 	}
> }
>
>  Is it a race condition or am I getting it horribly wrong?  Thx in
> advance.

Yes, it's a race. Actually a variant of the race that lead to the introduction of set_current_state():

test_bit is a simple read instruction. i386 cpus are free to execute it early, i.e. they can execute it before the write part of "++local_irq_count(cpu)".

I think smp_rmb() is the right barrier - could you write a patch and send it to Marcelo?

--
	Manfred



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