synchronize_irq needs at the very least a compiler barrier and a
read barrier on SMP, but there are enough cases around where a
write barrier is also needed and it's not a hot path so I prefer
using a full smp_mb() here.
It will degrade to a compiler barrier on !SMP.
Signed-off-by: Benjamin Herrenschmidt <email@example.com>
--- linux-work.orig/kernel/irq/manage.c 2007-10-18 11:22:16.000000000 +1000
+++ linux-work/kernel/irq/manage.c 2007-10-18 11:22:20.000000000 +1000
@@ -33,6 +33,7 @@ void synchronize_irq(unsigned int irq)
if (irq >= NR_IRQS)
while (desc->status & IRQ_INPROGRESS)