Re: Possible race condition in i386 global_irq_lock handling.

[Andrea Arcangeli <andrea@suse.de>]

thanks TeJun,

just one comment

On Fri, Aug 22, 2003 at 10:18:40AM +0900, TeJun Huh wrote:
>  3. remove irqs_running() test from synchronize_irq()

I'm not convinced this one is needed. An irq can still run on another
cpu but the cli();sti() may execute while it's here:

	irq running		synchronize_irq()
	--------------		-----------------
	do_IRQ
	handle_IRQ_event
				cli()
				sti()

	irq_enter -> way too late

in short, doing irqs_running() doesn't seem to weaken the semantics of
synchronize_irq() to me.

I think it should be changed this way instead:

void synchronize_irq(void)
{
	smp_mb();
	if (irqs_running()) {
		/* Stupid approach */
		cli();
		sti();
	}
}

to be sure to read the local irq area after the previous code (the
test_and_set_bit of the global_irq_lock of a cli() in your version would
achieve the same implicit smp_mb too, so maybe your only point for doing
cli()/sti() was to execute the smp_mb before the irqs_running?).  the
above version is more finegrined and it looks equivalent to yours.

Andrea