[PATCH] genirq: Wake IRQ threads immediately when changing affinity

[Crystal Wood]

This avoids a situation where the IRQs are being migrated away from
an isolated cpu, but the migration does not happen until some arbitrary
time in the future, causing an isolation disruption.

Note that this is of the most benefit on systems where the IRQ affinity
itself does not need to be deferred to the IRQ handler, but even where
that's not the case, the total dirsuption will be less.

Signed-off-by: Crystal Wood <crwood@xxxxxxxxxx>
---
 kernel/irq/manage.c | 112 +++++++++++++++++++++++---------------------
 1 file changed, 58 insertions(+), 54 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 1782f90cd8c6..9a8f2ecd575d 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -192,10 +192,14 @@ void irq_set_thread_affinity(struct irq_desc *desc)
 	struct irqaction *action;
 
 	for_each_action_of_desc(desc, action) {
-		if (action->thread)
+		if (action->thread) {
 			set_bit(IRQTF_AFFINITY, &action->thread_flags);
-		if (action->secondary && action->secondary->thread)
+			wake_up_process(action->thread);
+		}
+		if (action->secondary && action->secondary->thread) {
 			set_bit(IRQTF_AFFINITY, &action->secondary->thread_flags);
+			wake_up_process(action->secondary->thread);
+		}
 	}
 }
 
@@ -1049,10 +1053,60 @@ static irqreturn_t irq_forced_secondary_handler(int irq, void *dev_id)
 	return IRQ_NONE;
 }
 
-static int irq_wait_for_interrupt(struct irqaction *action)
+#ifdef CONFIG_SMP
+/*
+ * Check whether we need to change the affinity of the interrupt thread.
+ */
+static void
+irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action)
+{
+	cpumask_var_t mask;
+	bool valid = true;
+
+	if (!test_and_clear_bit(IRQTF_AFFINITY, &action->thread_flags))
+		return;
+
+	__set_current_state(TASK_RUNNING);
+
+	/*
+	 * In case we are out of memory we set IRQTF_AFFINITY again and
+	 * try again next time
+	 */
+	if (!alloc_cpumask_var(&mask, GFP_KERNEL)) {
+		set_bit(IRQTF_AFFINITY, &action->thread_flags);
+		return;
+	}
+
+	raw_spin_lock_irq(&desc->lock);
+	/*
+	 * This code is triggered unconditionally. Check the affinity
+	 * mask pointer. For CPU_MASK_OFFSTACK=n this is optimized out.
+	 */
+	if (cpumask_available(desc->irq_common_data.affinity)) {
+		const struct cpumask *m;
+
+		m = irq_data_get_effective_affinity_mask(&desc->irq_data);
+		cpumask_copy(mask, m);
+	} else {
+		valid = false;
+	}
+	raw_spin_unlock_irq(&desc->lock);
+
+	if (valid)
+		set_cpus_allowed_ptr(current, mask);
+	free_cpumask_var(mask);
+}
+#else
+static inline void
+irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action) { }
+#endif
+
+static int irq_wait_for_interrupt(struct irq_desc *desc,
+				  struct irqaction *action)
 {
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
+		irq_thread_check_affinity(desc, action);
 
 		if (kthread_should_stop()) {
 			/* may need to run one last time */
@@ -1129,52 +1183,6 @@ static void irq_finalize_oneshot(struct irq_desc *desc,
 	chip_bus_sync_unlock(desc);
 }
 
-#ifdef CONFIG_SMP
-/*
- * Check whether we need to change the affinity of the interrupt thread.
- */
-static void
-irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action)
-{
-	cpumask_var_t mask;
-	bool valid = true;
-
-	if (!test_and_clear_bit(IRQTF_AFFINITY, &action->thread_flags))
-		return;
-
-	/*
-	 * In case we are out of memory we set IRQTF_AFFINITY again and
-	 * try again next time
-	 */
-	if (!alloc_cpumask_var(&mask, GFP_KERNEL)) {
-		set_bit(IRQTF_AFFINITY, &action->thread_flags);
-		return;
-	}
-
-	raw_spin_lock_irq(&desc->lock);
-	/*
-	 * This code is triggered unconditionally. Check the affinity
-	 * mask pointer. For CPU_MASK_OFFSTACK=n this is optimized out.
-	 */
-	if (cpumask_available(desc->irq_common_data.affinity)) {
-		const struct cpumask *m;
-
-		m = irq_data_get_effective_affinity_mask(&desc->irq_data);
-		cpumask_copy(mask, m);
-	} else {
-		valid = false;
-	}
-	raw_spin_unlock_irq(&desc->lock);
-
-	if (valid)
-		set_cpus_allowed_ptr(current, mask);
-	free_cpumask_var(mask);
-}
-#else
-static inline void
-irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action) { }
-#endif
-
 /*
  * Interrupts which are not explicitly requested as threaded
  * interrupts rely on the implicit bh/preempt disable of the hard irq
@@ -1312,13 +1320,9 @@ static int irq_thread(void *data)
 	init_task_work(&on_exit_work, irq_thread_dtor);
 	task_work_add(current, &on_exit_work, TWA_NONE);
 
-	irq_thread_check_affinity(desc, action);
-
-	while (!irq_wait_for_interrupt(action)) {
+	while (!irq_wait_for_interrupt(desc, action)) {
 		irqreturn_t action_ret;
 
-		irq_thread_check_affinity(desc, action);
-
 		action_ret = handler_fn(desc, action);
 		if (action_ret == IRQ_WAKE_THREAD)
 			irq_wake_secondary(desc, action);
-- 
2.43.0