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SubjectRe: Possible race condition in i386 global_irq_lock handling.
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
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