linux-kernel - [PATCH v2] genirq: avoid long loops in handle_edge

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Date:   Mon, 25 Sep 2023 10:51:54 +0800
From:   Wei Gong <gongwei833x@...il.com>
To:     tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, Wei Gong <gongwei833x@...il.com>
Subject: [PATCH v2] genirq: avoid long loops in handle_edge_irq

When there are a large number of interrupts occurring on the tx
queue(irq smp_affinity=1) of the network card, changing the CPU
affinity of the tx queue (echo 2 > /proc/irq/xx/smp_affinity)
will cause handle_edge_irq to loop for a long time in the
do {} while() loop.

After setting the IRQ CPU affinity, the next interrupt will only
be activated when it arrives. Therefore, the next interrupt will
still be on CPU 0. When a new CPU affinity is activated on CPU 0,
subsequent interrupts will be processed on CPU 1.

       cpu 0                                cpu 1
  - handle_edge_irq
    - apic_ack_irq
      - irq_do_set_affinity
                                        - handle_edge_irq
    - do {
        - handle_irq_event
          - istate &= ~IRQS_PENDIN
          - IRQD_IRQ_INPROGRESS
          - spin_unlock()
                                          - spin_lock()
                                          - istate |= IRQS_PENDIN
          - handle_irq_event_percpu       - mask_ack_irq()
                                          - spin_unlock()
          - spin_unlock

      } while(IRQS_PENDIN &&
              !irq_disable)

Therefore, when determining whether to continue looping, we add a check
to see if the current CPU belongs to the affinity table of the interrupt.

Signed-off-by: Wei Gong <gongwei833x@...il.com>
---
 kernel/irq/chip.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index dc94e0bf2c94..6da455e1a692 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -831,7 +831,8 @@ void handle_edge_irq(struct irq_desc *desc)
 		handle_irq_event(desc);

 	} while ((desc->istate & IRQS_PENDING) &&
-		 !irqd_irq_disabled(&desc->irq_data));
+		 !irqd_irq_disabled(&desc->irq_data) &&
+		 cpumask_test_cpu(smp_processor_id(), irq_data_get_affinity_mask(&desc->irq_data)));

 out_unlock:
 	raw_spin_unlock(&desc->lock);
-- 
2.32.1 (Apple Git-133)