s390/qeth: fix potential deadlock on workqueue flush

The L2 bridgeport code uses the coarse 'conf_mutex' for guarding access
to its configuration state.
This can result in a deadlock when qeth_l2_stop_card() - called under the
conf_mutex - blocks on flush_workqueue() to wait for the completion of
pending bridgeport workers. Such workers would also need to aquire
the conf_mutex, stalling indefinitely.

Introduce a lock that specifically guards the bridgeport configuration,
so that the workers no longer need the conf_mutex.
Wrapping qeth_l2_promisc_to_bridge() in this fine-grained lock then also
fixes a theoretical race against a concurrent qeth_bridge_port_role_store()
operation.

Fixes: c0a2e4d10d93 ("s390/qeth: conclude all event processing before offlining a card")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 7 deletions

diff --git a/drivers/s390/net/qeth_l2_main.c b/drivers/s390/net/qeth_l2_main.c
index bd8143e51747..4bccdce19b5a 100644
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -467,10 +467,14 @@ static void qeth_l2_set_promisc_mode(struct qeth_card *card)
 	if (card->info.promisc_mode == enable)
 		return;
 
-	if (qeth_adp_supported(card, IPA_SETADP_SET_PROMISC_MODE))
+	if (qeth_adp_supported(card, IPA_SETADP_SET_PROMISC_MODE)) {
 		qeth_setadp_promisc_mode(card, enable);
-	else if (card->options.sbp.reflect_promisc)
-		qeth_l2_promisc_to_bridge(card, enable);
+	} else {
+		mutex_lock(&card->sbp_lock);
+		if (card->options.sbp.reflect_promisc)
+			qeth_l2_promisc_to_bridge(card, enable);
+		mutex_unlock(&card->sbp_lock);
+	}
 }
 
 /* New MAC address is added to the hash table and marked to be written on card
@@ -631,6 +635,7 @@ static int qeth_l2_probe_device(struct ccwgroup_device *gdev)
 	int rc;
 
 	qeth_l2_vnicc_set_defaults(card);
+	mutex_init(&card->sbp_lock);
 
 	if (gdev->dev.type == &qeth_generic_devtype) {
 		rc = qeth_l2_create_device_attributes(&gdev->dev);
@@ -804,10 +809,12 @@ static int qeth_l2_set_online(struct ccwgroup_device *gdev)
 	} else
 		card->info.hwtrap = 0;
 
+	mutex_lock(&card->sbp_lock);
 	qeth_bridgeport_query_support(card);
 	if (card->options.sbp.supported_funcs)
 		dev_info(&card->gdev->dev,
 		"The device represents a Bridge Capable Port\n");
+	mutex_unlock(&card->sbp_lock);
 
 	qeth_l2_register_dev_addr(card);
 
@@ -1162,9 +1169,9 @@ static void qeth_bridge_state_change_worker(struct work_struct *work)
 
 	/* Role should not change by itself, but if it did, */
 	/* information from the hardware is authoritative.  */
-	mutex_lock(&data->card->conf_mutex);
+	mutex_lock(&data->card->sbp_lock);
 	data->card->options.sbp.role = entry->role;
-	mutex_unlock(&data->card->conf_mutex);
+	mutex_unlock(&data->card->sbp_lock);
 
 	snprintf(env_locrem, sizeof(env_locrem), "BRIDGEPORT=statechange");
 	snprintf(env_role, sizeof(env_role), "ROLE=%s",
@@ -1230,9 +1237,9 @@ static void qeth_bridge_host_event_worker(struct work_struct *work)
 			: (data->hostevs.lost_event_mask == 0x02)
 			? "Bridge port state change"
 			: "Unknown reason");
-		mutex_lock(&data->card->conf_mutex);
+		mutex_lock(&data->card->sbp_lock);
 		data->card->options.sbp.hostnotification = 0;
-		mutex_unlock(&data->card->conf_mutex);
+		mutex_unlock(&data->card->sbp_lock);
 		qeth_bridge_emit_host_event(data->card, anev_abort,
 			0, NULL, NULL);
 	} else