s390/qeth: fix locking for discipline setup / removal

Due to insufficient locking, qeth_core_set_online() and
qeth_dev_layer2_store() can run in parallel, both attempting to load &
setup the discipline (and stepping on each other toes along the way).
A similar race can also occur between qeth_core_remove_device() and
qeth_dev_layer2_store().

Access to .discipline is meant to be protected by the discipline_mutex,
so add/expand the locking in qeth_core_remove_device() and
qeth_core_set_online().
Adjust the locking in qeth_l*_remove_device() accordingly, as it's now
handled by the callers in a consistent manner.

Based on an initial patch by Ursula Braun.

Fixes: 9dc48ccc68 ("qeth: serialize sysfs-triggered device configurations")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/s390/net/qeth_core_main.c

@@ -6585,6 +6585,7 @@ static int qeth_core_probe_device(struct ccwgroup_device *gdev)
 		break;
 	default:
 		card->info.layer_enforced = true;
+		/* It's so early that we don't need the discipline_mutex yet. */
 		rc = qeth_core_load_discipline(card, enforced_disc);
 		if (rc)
 			goto err_load;
@@ -6617,10 +6618,12 @@ static void qeth_core_remove_device(struct ccwgroup_device *gdev)
 
 	QETH_CARD_TEXT(card, 2, "removedv");
 
+	mutex_lock(&card->discipline_mutex);
 	if (card->discipline) {
 		card->discipline->remove(gdev);
 		qeth_core_free_discipline(card);
 	}
+	mutex_unlock(&card->discipline_mutex);
 
 	qeth_free_qdio_queues(card);
 
@@ -6635,6 +6638,7 @@ static int qeth_core_set_online(struct ccwgroup_device *gdev)
 	int rc = 0;
 	enum qeth_discipline_id def_discipline;
 
+	mutex_lock(&card->discipline_mutex);
 	if (!card->discipline) {
 		def_discipline = IS_IQD(card) ? QETH_DISCIPLINE_LAYER3 :
 						QETH_DISCIPLINE_LAYER2;
@@ -6648,11 +6652,10 @@ static int qeth_core_set_online(struct ccwgroup_device *gdev)
 		}
 	}
 
-	mutex_lock(&card->discipline_mutex);
 	rc = qeth_set_online(card, card->discipline);
-	mutex_unlock(&card->discipline_mutex);
 
 err:
+	mutex_unlock(&card->discipline_mutex);
 	return rc;
 }
 

drivers/s390/net/qeth_l2_main.c

@@ -2207,11 +2207,8 @@ static void qeth_l2_remove_device(struct ccwgroup_device *gdev)
 	qeth_set_allowed_threads(card, 0, 1);
 	wait_event(card->wait_q, qeth_threads_running(card, 0xffffffff) == 0);
 
-	if (gdev->state == CCWGROUP_ONLINE) {
-		mutex_lock(&card->discipline_mutex);
+	if (gdev->state == CCWGROUP_ONLINE)
 		qeth_set_offline(card, card->discipline, false);
-		mutex_unlock(&card->discipline_mutex);
-	}
 
 	cancel_work_sync(&card->close_dev_work);
 	if (card->dev->reg_state == NETREG_REGISTERED)

drivers/s390/net/qeth_l3_main.c

@@ -1970,11 +1970,8 @@ static void qeth_l3_remove_device(struct ccwgroup_device *cgdev)
 	qeth_set_allowed_threads(card, 0, 1);
 	wait_event(card->wait_q, qeth_threads_running(card, 0xffffffff) == 0);
 
-	if (cgdev->state == CCWGROUP_ONLINE) {
-		mutex_lock(&card->discipline_mutex);
+	if (cgdev->state == CCWGROUP_ONLINE)
 		qeth_set_offline(card, card->discipline, false);
-		mutex_unlock(&card->discipline_mutex);
-	}
 
 	cancel_work_sync(&card->close_dev_work);
 	if (card->dev->reg_state == NETREG_REGISTERED)