From: Julian Wiedmann <jwi@linux.ibm.com>
Date: Thu, 7 Jan 2021 18:24:41 +0100
Subject: s390/qeth: fix locking for discipline setup / removal
Git-commit: b41b554c1ee75070a14c02a88496b1f231c7eacc
Patch-mainline: v5.11-rc3
References: git-fixes

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: 9dc48ccc68b9 ("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>
[ ptesarik: Since SLE15-SP1 still contains pm callbacks, appropriate
  locking must be added there. ]
Signed-off-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/s390/net/qeth_core_main.c |   28 ++++++++++++++++++++--------
 drivers/s390/net/qeth_l2_main.c   |    5 +----
 drivers/s390/net/qeth_l3_main.c   |    5 +----
 3 files changed, 22 insertions(+), 16 deletions(-)

--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -5869,6 +5869,7 @@ static int qeth_core_probe_device(struct
 		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;
@@ -5904,10 +5905,12 @@ static void qeth_core_remove_device(stru
 
 	QETH_DBF_TEXT(SETUP, 2, "removedv");
 
+	mutex_lock(&card->discipline_mutex);
 	if (card->discipline) {
 		card->discipline->remove(gdev);
 		qeth_core_free_discipline(card);
 	}
+	mutex_unlock(&card->discipline_mutex);
 
 	write_lock_irq(&qeth_core_card_list.rwlock);
 	list_del(&card->list);
@@ -5923,6 +5926,7 @@ static int qeth_core_set_online(struct c
 	int rc = 0;
 	enum qeth_discipline_id def_discipline;
 
+	mutex_lock(&card->discipline_mutex);
 	if (!card->discipline) {
 		if (card->info.type == QETH_CARD_TYPE_IQD)
 			def_discipline = QETH_DISCIPLINE_LAYER3;
@@ -5938,11 +5942,10 @@ static int qeth_core_set_online(struct c
 		}
 	}
 
-	mutex_lock(&card->discipline_mutex);
 	rc = card->discipline->set_online(gdev);
-	mutex_unlock(&card->discipline_mutex);
 
 err:
+	mutex_unlock(&card->discipline_mutex);
 	return rc;
 }
 
@@ -5972,25 +5975,34 @@ static void qeth_core_shutdown(struct cc
 static int qeth_core_freeze(struct ccwgroup_device *gdev)
 {
 	struct qeth_card *card = dev_get_drvdata(&gdev->dev);
+	int rc = 0;
+	mutex_lock(&card->discipline_mutex);
 	if (card->discipline && card->discipline->freeze)
-		return card->discipline->freeze(gdev);
-	return 0;
+		rc = card->discipline->freeze(gdev);
+	mutex_unlock(&card->discipline_mutex);
+	return rc;
 }
 
 static int qeth_core_thaw(struct ccwgroup_device *gdev)
 {
 	struct qeth_card *card = dev_get_drvdata(&gdev->dev);
+	int rc = 0;
+	mutex_lock(&card->discipline_mutex);
 	if (card->discipline && card->discipline->thaw)
-		return card->discipline->thaw(gdev);
-	return 0;
+		rc = card->discipline->thaw(gdev);
+	mutex_unlock(&card->discipline_mutex);
+	return rc;
 }
 
 static int qeth_core_restore(struct ccwgroup_device *gdev)
 {
 	struct qeth_card *card = dev_get_drvdata(&gdev->dev);
+	int rc = 0;
+	mutex_lock(&card->discipline_mutex);
 	if (card->discipline && card->discipline->restore)
-		return card->discipline->restore(gdev);
-	return 0;
+		rc = card->discipline->restore(gdev);
+	mutex_unlock(&card->discipline_mutex);
+	return rc;
 }
 
 static ssize_t group_store(struct device_driver *ddrv, const char *buf,
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -825,11 +825,8 @@ static void qeth_l2_remove_device(struct
 	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_l2_set_offline(cgdev);
-		mutex_unlock(&card->discipline_mutex);
-	}
 
 	cancel_work_sync(&card->close_dev_work);
 	if (qeth_netdev_is_registered(card->dev))
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -2475,11 +2475,8 @@ static void qeth_l3_remove_device(struct
 	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_l3_set_offline(cgdev);
-		mutex_unlock(&card->discipline_mutex);
-	}
 
 	cancel_work_sync(&card->close_dev_work);
 	if (qeth_netdev_is_registered(card->dev))