net: sched: make newly activated qdiscs visible

In their .attach callback, mq[prio] only add the qdiscs of the currently
active TX queues to the device's qdisc hash list.
If a user later increases the number of active TX queues, their qdiscs
are not visible via eg. 'tc qdisc show'.

Add a hook to netif_set_real_num_tx_queues() that walks all active
TX queues and adds those which are missing to the hash list.

CC: Eric Dumazet <edumazet@google.com>
CC: Jamal Hadi Salim <jhs@mojatatu.com>
CC: Cong Wang <xiyou.wangcong@gmail.com>
CC: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sch_generic.h

@@ -153,6 +153,11 @@ static inline bool qdisc_is_empty(const struct Qdisc *qdisc)
 	return !READ_ONCE(qdisc->q.qlen);
 }
 
+static inline bool qdisc_hashed(struct Qdisc *qdisc)
+{
+	return hash_hashed(&qdisc->hash);
+}
+
 static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 {
 	if (qdisc->flags & TCQ_F_NOLOCK) {
@@ -629,6 +634,7 @@ void qdisc_class_hash_grow(struct Qdisc *, struct Qdisc_class_hash *);
 void qdisc_class_hash_destroy(struct Qdisc_class_hash *);
 
 int dev_qdisc_change_tx_queue_len(struct net_device *dev);
+void dev_qdisc_set_real_num_tx_queues(struct net_device *dev);
 void dev_init_scheduler(struct net_device *dev);
 void dev_shutdown(struct net_device *dev);
 void dev_activate(struct net_device *dev);

net/core/dev.c

@@ -2875,6 +2875,7 @@ int netif_set_real_num_tx_queues(struct net_device *dev, unsigned int txq)
 			netif_setup_tc(dev, txq);
 
 		dev->real_num_tx_queues = txq;
+		dev_qdisc_set_real_num_tx_queues(dev);
 
 		if (disabling) {
 			synchronize_net();

net/sched/sch_generic.c

@@ -1268,6 +1268,27 @@ int dev_qdisc_change_tx_queue_len(struct net_device *dev)
 	return ret;
 }
 
+void dev_qdisc_set_real_num_tx_queues(struct net_device *dev)
+{
+#ifdef CONFIG_NET_SCHED
+	struct Qdisc *sch = dev->qdisc;
+	unsigned int ntx;
+
+	if (!sch)
+		return;
+
+	ASSERT_RTNL();
+
+	for (ntx = 0; ntx < dev->real_num_tx_queues; ntx++) {
+		struct netdev_queue *dev_queue = netdev_get_tx_queue(dev, ntx);
+		struct Qdisc *qdisc = dev_queue->qdisc;
+
+		if (qdisc && !qdisc_hashed(qdisc))
+			qdisc_hash_add(qdisc, false);
+	}
+#endif
+}
+
 static void dev_init_scheduler_queue(struct net_device *dev,
 				     struct netdev_queue *dev_queue,
 				     void *_qdisc)