[PATCH] irq_work: Migrate the remaining work of the offline CPU on PREEMPT_RT

[Zqiang]

When CPU goes offline and invoke CPU_DYING callbacks, the
smpcfd_dying_cpu() be invoked to flush the remaining irq_work of the
offline CPU, for lazy irq_work, will wakeup per-CPU irq_work kthreads
to invoke callbacks, but the irq_work kthreads are in TASK_PARKED
state, will not get the actual wakeup, resulting in the remaining lazy
irq_work not being executed.

This commit requeue remaining of lazy irq_work to online CPU.

Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
---
 include/linux/irq_work.h |  1 +
 kernel/cpu.c             |  1 +
 kernel/irq_work.c        | 20 ++++++++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index 8cd11a223260..900d9053a62d 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -66,6 +66,7 @@ void irq_work_sync(struct irq_work *work);
 void irq_work_run(void);
 bool irq_work_needs_cpu(void);
 void irq_work_single(void *arg);
+void irq_work_migrate(int cpu);
 #else
 static inline bool irq_work_needs_cpu(void) { return false; }
 static inline void irq_work_run(void) { }
diff --git a/kernel/cpu.c b/kernel/cpu.c
index bbad5e375d3b..70461b6d785d 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1075,6 +1075,7 @@ static int takedown_cpu(unsigned int cpu)
 
 	tick_cleanup_dead_cpu(cpu);
 	rcutree_migrate_callbacks(cpu);
+	irq_work_migrate(cpu);
 	return 0;
 }
 
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 7afa40fe5cc4..bfa21468c2df 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -242,6 +242,26 @@ static void irq_work_run_list(struct llist_head *list)
 		irq_work_single(work);
 }
 
+void irq_work_migrate(int cpu)
+{
+	struct irq_work *work, *tmp;
+	struct llist_node *llnode;
+	struct llist_head *list = per_cpu_ptr(&lazy_list, cpu);
+
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		return;
+
+	if (llist_empty(list))
+		return;
+
+	llnode = llist_del_all(list);
+	llist_for_each_entry_safe(work, tmp, llnode, node.llist) {
+		atomic_set(&work->node.a_flags, 0);
+		irq_work_queue(work);
+	}
+}
+EXPORT_SYMBOL_GPL(irq_work_migrate);
+
 /*
  * hotplug calls this through:
  *  hotplug_cfd() -> flush_smp_call_function_queue()
-- 
2.25.1