genirq: Wake interrupt threads immediately when changing affinity

The affinity setting of interrupt threads happens in the context of the
thread when the thread is woken up by an hard interrupt. As this can be an
arbitrary after changing the affinity, the thread can become runnable on an
isolated CPU and cause isolation disruption.

Avoid this by checking the set affinity request in wait_for_interrupt() and
waking the threads immediately when the affinity is modified.

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

Signed-off-by: Crystal Wood <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

kernel/irq/manage.c

···
 	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);
+		}
 	}
 }
 
···
 	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 = false;
+
+	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);
+		valid = true;
+	}
+	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 */
···
 	raw_spin_unlock_irq(&desc->lock);
 	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
···
 	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)