x86: Fix interrupt leak due to migration

When we migrate an interrupt from one CPU to another, we set the move_in_progress flag and clean up the vectors later once they're not being used. If you're unlucky and call destroy_irq() before the vectors become un-used, the move_in_progress flag is never cleared, which causes the interrupt to become unusable.

This was discovered by Jesse Brandeburg for whom it manifested as an MSI-X device refusing to use MSI-X mode when the driver was unloaded and reloaded repeatedly.

index 7a3f202..c9513e1 100644
@@ -1140,6 +1140,20 @@ static void __clear_irq_vector(int irq)
 
 	cfg->vector = 0;
 	cpus_clear(cfg->domain);
+
+	if (likely(!cfg->move_in_progress))
+		return;
+	cpus_and(mask, cfg->old_domain, cpu_online_map);
+	for_each_cpu_mask_nr(cpu, mask) {
+		for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS;
+								vector++) {
+			if (per_cpu(vector_irq, cpu)[vector] != irq)
+				continue;
+			per_cpu(vector_irq, cpu)[vector] = -1;
+			break;
+		}
+	}
+	cfg->move_in_progress = 0;
 }
 
 void __setup_vector_irq(int cpu)

Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

We did some other quick testing on this and it seems good. Thanks and good work Matthew!