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>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/s390/net/qeth_core_main.c |    7 +++++--
 drivers/s390/net/qeth_l2_main.c   |    5 +----
 drivers/s390/net/qeth_l3_main.c   |    5 +----
 3 files changed, 7 insertions(+), 10 deletions(-)

--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -6363,6 +6363,7 @@ 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;
@@ -6395,10 +6396,12 @@ static void qeth_core_remove_device(stru
 
 	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);
 
@@ -6413,6 +6416,7 @@ 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) {
 		def_discipline = IS_IQD(card) ? QETH_DISCIPLINE_LAYER3 :
 						QETH_DISCIPLINE_LAYER2;
@@ -6426,11 +6430,10 @@ static int qeth_core_set_online(struct c
 		}
 	}
 
-	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;
 }
 
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -2204,11 +2204,8 @@ 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 (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)
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -1973,11 +1973,8 @@ 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_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)