[RFC PATCH v2 2/4] irq/spurious: Account for multiple handles in note_interrupt

Leonardo Bras
2024-02-16T08:00:30Z

Currently note_interrupt() will check threads_handled for changes and use
it to mark an IRQ as handled, in order to avoid having a threaded
interrupt to falsely trigger unhandled IRQ detection.

This detection can still be falsely triggered if we have many IRQ handled
accounted between each check of threads_handled, as those will be counted
as a single one in the unhandled IRQ detection.

In order to fix this, subtract from irqs_unhandled the number of IRQs
handled since the last check (threads_handled_last - threads_handled).

Signed-off-by: Leonardo Bras <leobras@redhat.com>
---
include/linux/irqdesc.h | 2 +-
kernel/irq/spurious.c | 53 ++++++++++++++++++++++++++---------------
2 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index 62aff209315fe..957ac02e9ec2b 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -67,7 +67,7 @@ struct irq_desc {
unsigned long last_unhandled; /* Aging timer for unhandled count */
unsigned int irqs_unhandled;
atomic_t threads_handled;
- int threads_handled_last;
+ unsigned int threads_handled_last;
raw_spinlock_t lock;
struct cpumask *percpu_enabled;
const struct cpumask *percpu_affinity;
diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
index d92f33b2e31ee..4e8e2727b8beb 100644
--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -267,6 +267,28 @@ try_misrouted_irq(unsigned int irq, struct irq_desc *desc,
return action && (action->flags & IRQF_IRQPOLL);
}

+static inline int get_handled_diff(struct irq_desc *desc)
+{
+ unsigned int handled;
+ int diff;
+
+ handled = (unsigned int)atomic_read(&desc->threads_handled);
+ handled |= SPURIOUS_DEFERRED;
+
+ diff = handled - desc->threads_handled_last;
+ diff >>= SPURIOUS_DEFERRED_SHIFT;
+
+ /*
+ * Note: We keep the SPURIOUS_DEFERRED bit set. We are handling the
+ * previous invocation right now. Keep it for the current one, so the
+ * next hardware interrupt will account for it.
+ */
+ if (diff != 0)
+ desc->threads_handled_last = handled;
+
+ return diff;
+}
+
void note_interrupt(struct irq_desc *desc, irqreturn_t action_ret)
{
unsigned int irq;
@@ -308,7 +330,7 @@ void note_interrupt(struct irq_desc *desc, irqreturn_t action_ret)
* interrupt.
*/
if (action_ret == IRQ_WAKE_THREAD) {
- int handled;
+ int diff;
/*
* We use bit 0 of thread_handled_last to
* denote the deferred spurious detection
@@ -325,27 +347,20 @@ void note_interrupt(struct irq_desc *desc, irqreturn_t action_ret)
* Check whether one of the threaded handlers
* returned IRQ_HANDLED since the last
* interrupt happened.
- *
- * For simplicity we just set bit 0, as it is
- * set in threads_handled_last as well. So we
- * avoid extra masking. And we really do not
- * care about the high bits of the handled
- * count. We just care about the count being
- * different than the one we saw before.
*/
- handled = atomic_read(&desc->threads_handled);
- handled |= SPURIOUS_DEFERRED;
- if (handled != desc->threads_handled_last) {
- action_ret = IRQ_HANDLED;
+ diff = get_handled_diff(desc);
+ if (diff > 0) {
/*
- * Note: We keep the SPURIOUS_DEFERRED
- * bit set. We are handling the
- * previous invocation right now.
- * Keep it for the current one, so the
- * next hardware interrupt will
- * account for it.
+ * Subtract from irqs_unhandled the number of
+ * IRQs handled since the last change in
+ * threads_handled.
*/
- desc->threads_handled_last = handled;
+ if (diff < desc->irqs_unhandled)
+ desc->irqs_unhandled -= diff;
+ else
+ desc->irqs_unhandled = 0;
+
+ action_ret = IRQ_HANDLED;
} else {
/*
* None of the threaded handlers felt
--
2.43.2