[PATCH v2] kthread_worker: re-set CPU affinities if CPU come online

[qiang.zhang@windriver.com]

From: Zqiang <qiang.zhang@windriver.com>

When someone CPU offlined, the 'kthread_worker' which bind this CPU,
will run anywhere, if this CPU online, recovery of 'kthread_worker'
affinity by cpuhp notifiers.

Signed-off-by: Zqiang <qiang.zhang@windriver.com>
---
 v1->v2:
 rename variable kworker_online to kthread_worker_online.
 add 'cpuhp_node' and 'bind_cpu' init in KTHREAD_WORKER_INIT.
 add a comment explaining for WARN_ON_ONCE.

 include/linux/kthread.h |  4 ++++
 kernel/kthread.c        | 36 +++++++++++++++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 65b81e0c494d..c28963e87b18 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -93,6 +93,8 @@ struct kthread_worker {
 	struct list_head	delayed_work_list;
 	struct task_struct	*task;
 	struct kthread_work	*current_work;
+	struct hlist_node       cpuhp_node;
+	int                     bind_cpu;
 };
 
 struct kthread_work {
@@ -112,6 +114,8 @@ struct kthread_delayed_work {
 	.lock = __RAW_SPIN_LOCK_UNLOCKED((worker).lock),		\
 	.work_list = LIST_HEAD_INIT((worker).work_list),		\
 	.delayed_work_list = LIST_HEAD_INIT((worker).delayed_work_list),\
+	.cpuhp_node = {.next = NULL, .pprev = NULL},			\
+	.bind_cpu = -1,							\
 	}
 
 #define KTHREAD_WORK_INIT(work, fn)	{				\
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 34516b0a6eb7..6c66df585225 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -28,8 +28,10 @@
 #include <linux/uaccess.h>
 #include <linux/numa.h>
 #include <linux/sched/isolation.h>
+#include <linux/cpu.h>
 #include <trace/events/sched.h>
 
+static enum cpuhp_state kthread_worker_online;
 
 static DEFINE_SPINLOCK(kthread_create_lock);
 static LIST_HEAD(kthread_create_list);
@@ -649,6 +651,8 @@ void __kthread_init_worker(struct kthread_worker *worker,
 	lockdep_set_class_and_name(&worker->lock, key, name);
 	INIT_LIST_HEAD(&worker->work_list);
 	INIT_LIST_HEAD(&worker->delayed_work_list);
+	worker->bind_cpu = -1;
+	INIT_HLIST_NODE(&worker->cpuhp_node);
 }
 EXPORT_SYMBOL_GPL(__kthread_init_worker);
 
@@ -744,8 +748,11 @@ __kthread_create_worker(int cpu, unsigned int flags,
 	if (IS_ERR(task))
 		goto fail_task;
 
-	if (cpu >= 0)
+	if (cpu >= 0) {
+		cpuhp_state_add_instance_nocalls(kthread_worker_online, &worker->cpuhp_node);
 		kthread_bind(task, cpu);
+		worker->bind_cpu = cpu;
+	}
 
 	worker->flags = flags;
 	worker->task = task;
@@ -1230,6 +1237,9 @@ void kthread_destroy_worker(struct kthread_worker *worker)
 	if (WARN_ON(!task))
 		return;
 
+	if (worker->bind_cpu >= 0)
+		cpuhp_state_remove_instance_nocalls(kthread_worker_online, &worker->cpuhp_node);
+
 	kthread_flush_worker(worker);
 	kthread_stop(task);
 	WARN_ON(!list_empty(&worker->work_list));
@@ -1237,6 +1247,30 @@ void kthread_destroy_worker(struct kthread_worker *worker)
 }
 EXPORT_SYMBOL(kthread_destroy_worker);
 
+static int kthread_worker_cpu_online(unsigned int cpu, struct hlist_node *node)
+{
+	struct kthread_worker *worker = hlist_entry(node, struct kthread_worker, cpuhp_node);
+	struct task_struct *task = worker->task;
+
+	/* as we're called from CPU_ONLINE, the following shouldn't fail */
+	if (cpu == worker->bind_cpu)
+		WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpumask_of(cpu)) < 0);
+	return 0;
+}
+
+static __init int kthread_worker_hotplug_init(void)
+{
+	int ret;
+
+	ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "kthread-worker/online",
+					kthread_worker_cpu_online, NULL);
+	if (ret < 0)
+		return ret;
+	kthread_worker_online = ret;
+	return 0;
+}
+core_initcall(kthread_worker_hotplug_init);
+
 /**
  * kthread_use_mm - make the calling kthread operate on an address space
  * @mm: address space to operate on
-- 
2.17.1