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 <tglx@linutronix.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Link: http://lkml.kernel.org/r/20170619235447.431321047@linutronix.de

diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
index b7964e72ded7171ad23089e4134c9aaa1ec61a69..aee8f7ec40af259d605b370fe22045c589180f25 100644 (file)
--- a/kernel/irq/cpuhotplug.c
+++ b/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);
 }