s390/qeth: conclude all event processing before offlining a card

Work for Bridgeport events is currently placed on a driver-wide
workqueue. If the card is removed and freed while any such work is still
active, this causes a use-after-free.
So put the events on a per-card queue, where we can control their
lifetime. As we also don't want stale events to last beyond an
offline & online cycle, flush this queue when setting the card offline.

Fixes: b4d72c08b358 ("qeth: bridgeport support - basic control")
Signed-off-by: Julian Wiedmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/s390/net/qeth_core.h

···
 	struct qeth_seqno seqno;
 	struct qeth_card_options options;
 
+	struct workqueue_struct *event_wq;
 	wait_queue_head_t wait_q;
 	spinlock_t mclock;
 	unsigned long active_vlans[BITS_TO_LONGS(VLAN_N_VID)];
···
 extern const struct attribute_group qeth_device_attr_group;
 extern const struct attribute_group qeth_device_blkt_group;
 extern const struct device_type qeth_generic_devtype;
-extern struct workqueue_struct *qeth_wq;
 
 int qeth_card_hw_is_reachable(struct qeth_card *);
 const char *qeth_get_cardname_short(struct qeth_card *);

drivers/s390/net/qeth_core_main.c

···
 static void qeth_release_skbs(struct qeth_qdio_out_buffer *buf);
 static int qeth_init_qdio_out_buf(struct qeth_qdio_out_q *, int);
 
-struct workqueue_struct *qeth_wq;
-EXPORT_SYMBOL_GPL(qeth_wq);
+static struct workqueue_struct *qeth_wq;
 
 int qeth_card_hw_is_reachable(struct qeth_card *card)
 {
···
 	CARD_RDEV(card) = gdev->cdev[0];
 	CARD_WDEV(card) = gdev->cdev[1];
 	CARD_DDEV(card) = gdev->cdev[2];
+
+	card->event_wq = alloc_ordered_workqueue("%s", 0, dev_name(&gdev->dev));
+	if (!card->event_wq)
+		goto out_wq;
 	if (qeth_setup_channel(&card->read, true))
 		goto out_ip;
 	if (qeth_setup_channel(&card->write, true))
···
 out_channel:
 	qeth_clean_channel(&card->read);
 out_ip:
+	destroy_workqueue(card->event_wq);
+out_wq:
 	dev_set_drvdata(&gdev->dev, NULL);
 	kfree(card);
 out:
···
 	qeth_clean_channel(&card->read);
 	qeth_clean_channel(&card->write);
 	qeth_clean_channel(&card->data);
+	destroy_workqueue(card->event_wq);
 	qeth_free_qdio_buffers(card);
 	unregister_service_level(&card->qeth_service_level);
 	dev_set_drvdata(&card->gdev->dev, NULL);

drivers/s390/net/qeth_l2_main.c

···
 		qeth_clear_cmd_buffers(&card->read);
 		qeth_clear_cmd_buffers(&card->write);
 	}
+
+	flush_workqueue(card->event_wq);
 }
 
 static int qeth_l2_process_inbound_buffer(struct qeth_card *card,
···
 	data->card = card;
 	memcpy(&data->qports, qports,
 			sizeof(struct qeth_sbp_state_change) + extrasize);
-	queue_work(qeth_wq, &data->worker);
+	queue_work(card->event_wq, &data->worker);
 }
 
 struct qeth_bridge_host_data {
···
 	data->card = card;
 	memcpy(&data->hostevs, hostevs,
 			sizeof(struct qeth_ipacmd_addr_change) + extrasize);
-	queue_work(qeth_wq, &data->worker);
+	queue_work(card->event_wq, &data->worker);
 }
 
 /* SETBRIDGEPORT support; sending commands */

drivers/s390/net/qeth_l3_main.c

···
 		qeth_clear_cmd_buffers(&card->read);
 		qeth_clear_cmd_buffers(&card->write);
 	}
+
+	flush_workqueue(card->event_wq);
 }
 
 /*