RDMA/core: Avoid flush_workqueue(system_unbound_wq) usage

Flushing system-wide workqueues is dangerous and will be forbidden.
Replace system_unbound_wq with local ib_unreg_wq.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Tetsuo Handa <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/infiniband/core/device.c

···
 struct workqueue_struct *ib_comp_unbound_wq;
 struct workqueue_struct *ib_wq;
 EXPORT_SYMBOL_GPL(ib_wq);
+static struct workqueue_struct *ib_unreg_wq;
 
 /*
  * Each of the three rwsem locks (devices, clients, client_data) protects the
···
 	WARN_ON(!refcount_read(&ib_dev->refcount));
 	WARN_ON(!ib_dev->ops.dealloc_driver);
 	get_device(&ib_dev->dev);
-	if (!queue_work(system_unbound_wq, &ib_dev->unregistration_work))
+	if (!queue_work(ib_unreg_wq, &ib_dev->unregistration_work))
 		put_device(&ib_dev->dev);
 }
 EXPORT_SYMBOL(ib_unregister_device_queued);
···
 
 static int __init ib_core_init(void)
 {
-	int ret;
+	int ret = -ENOMEM;
 
 	ib_wq = alloc_workqueue("infiniband", 0, 0);
 	if (!ib_wq)
 		return -ENOMEM;
 
+	ib_unreg_wq = alloc_workqueue("ib-unreg-wq", WQ_UNBOUND,
+				      WQ_UNBOUND_MAX_ACTIVE);
+	if (!ib_unreg_wq)
+		goto err;
+
 	ib_comp_wq = alloc_workqueue("ib-comp-wq",
 			WQ_HIGHPRI | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
-	if (!ib_comp_wq) {
-		ret = -ENOMEM;
-		goto err;
-	}
+	if (!ib_comp_wq)
+		goto err_unbound;
 
 	ib_comp_unbound_wq =
 		alloc_workqueue("ib-comp-unb-wq",
 				WQ_UNBOUND | WQ_HIGHPRI | WQ_MEM_RECLAIM |
 				WQ_SYSFS, WQ_UNBOUND_MAX_ACTIVE);
-	if (!ib_comp_unbound_wq) {
-		ret = -ENOMEM;
+	if (!ib_comp_unbound_wq)
 		goto err_comp;
-	}
 
 	ret = class_register(&ib_class);
 	if (ret) {
···
 	destroy_workqueue(ib_comp_unbound_wq);
 err_comp:
 	destroy_workqueue(ib_comp_wq);
+err_unbound:
+	destroy_workqueue(ib_unreg_wq);
 err:
 	destroy_workqueue(ib_wq);
 	return ret;
···
 	destroy_workqueue(ib_comp_wq);
 	/* Make sure that any pending umem accounting work is done. */
 	destroy_workqueue(ib_wq);
-	flush_workqueue(system_unbound_wq);
+	destroy_workqueue(ib_unreg_wq);
 	WARN_ON(!xa_empty(&clients));
 	WARN_ON(!xa_empty(&devices));
 }