qeth: synchronize discipline module loading

During system startup udev may try to configure devices in
parallel so we have to synchronize discipline module
loading.

Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_core_main.c

@@ -51,6 +51,7 @@ static struct kmem_cache *qeth_qdio_outbuf_cache;
 static struct device *qeth_core_root_dev;
 static unsigned int known_devices[][6] = QETH_MODELLIST_ARRAY;
 static struct lock_class_key qdio_out_skb_queue_key;
+static struct mutex qeth_mod_mutex;
 
 static void qeth_send_control_data_cb(struct qeth_channel *,
 			struct qeth_cmd_buffer *);
@@ -5040,6 +5041,7 @@ int qeth_core_load_discipline(struct qeth_card *card,
 		enum qeth_discipline_id discipline)
 {
 	int rc = 0;
+	mutex_lock(&qeth_mod_mutex);
 	switch (discipline) {
 	case QETH_DISCIPLINE_LAYER3:
 		card->discipline.ccwgdriver = try_then_request_module(
@@ -5057,6 +5059,7 @@ int qeth_core_load_discipline(struct qeth_card *card,
 			"support discipline %d\n", discipline);
 		rc = -EINVAL;
 	}
+	mutex_unlock(&qeth_mod_mutex);
 	return rc;
 }
 
@@ -5540,6 +5543,7 @@ static int __init qeth_core_init(void)
 	pr_info("loading core functions\n");
 	INIT_LIST_HEAD(&qeth_core_card_list.list);
 	rwlock_init(&qeth_core_card_list.rwlock);
+	mutex_init(&qeth_mod_mutex);
 
 	rc = qeth_register_dbf_views();
 	if (rc)