genirq/cpuhotplug: Avoid irq affinity setting for single targets

Avoid trying to add a newly online CPU to the effective affinity mask of an
started up interrupt. That interrupt will either stay on the already online
CPU or move around for no value.

Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Keith Busch <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]

Author: KAGA-KOKO

kernel/irq/cpuhotplug.c

@@ -148,9 +148,17 @@ static void irq_restore_affinity_of_irq(struct irq_desc *desc, unsigned int cpu)
 	    !irq_data_get_irq_chip(data) || !cpumask_test_cpu(cpu, affinity))
 		return;
 
-	if (irqd_is_managed_and_shutdown(data))
+	if (irqd_is_managed_and_shutdown(data)) {
 		irq_startup(desc, IRQ_RESEND, IRQ_START_COND);
-	else
+		return;
+	}
+
+	/*
+	 * If the interrupt can only be directed to a single target
+	 * CPU then it is already assigned to a CPU in the affinity
+	 * mask. No point in trying to move it around.
+	 */
+	if (!irqd_is_single_target(data))
 		irq_set_affinity_locked(data, affinity, false);
 }