net: qdisc: use rcu prefix and silence sparse warnings

Add __rcu notation to qdisc handling by doing this we can make
smatch output more legible. And anyways some of the cases should
be using rcu_dereference() see qdisc_all_tx_empty(),
qdisc_tx_chainging(), and so on.

Also *wake_queue() API is commonly called from driver timer routines
without rcu lock or rtnl lock. So I added rcu_read_lock() blocks
around netif_wake_subqueue and netif_tx_wake_queue.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index ba72f6b..ae721f5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -543,7 +543,7 @@
  * read mostly part
  */
 	struct net_device	*dev;
-	struct Qdisc		*qdisc;
+	struct Qdisc __rcu	*qdisc;
 	struct Qdisc		*qdisc_sleeping;
 #ifdef CONFIG_SYSFS
 	struct kobject		kobj;
@@ -2356,12 +2356,7 @@
 DECLARE_PER_CPU_ALIGNED(struct softnet_data, softnet_data);
 
 void __netif_schedule(struct Qdisc *q);
-
-static inline void netif_schedule_queue(struct netdev_queue *txq)
-{
-	if (!(txq->state & QUEUE_STATE_ANY_XOFF))
-		__netif_schedule(txq->qdisc);
-}
+void netif_schedule_queue(struct netdev_queue *txq);
 
 static inline void netif_tx_schedule_all(struct net_device *dev)
 {
@@ -2397,11 +2392,7 @@
 	}
 }
 
-static inline void netif_tx_wake_queue(struct netdev_queue *dev_queue)
-{
-	if (test_and_clear_bit(__QUEUE_STATE_DRV_XOFF, &dev_queue->state))
-		__netif_schedule(dev_queue->qdisc);
-}
+void netif_tx_wake_queue(struct netdev_queue *dev_queue);
 
 /**
  *	netif_wake_queue - restart transmit
@@ -2673,19 +2664,7 @@
 	return __netif_subqueue_stopped(dev, skb_get_queue_mapping(skb));
 }
 
-/**
- *	netif_wake_subqueue - allow sending packets on subqueue
- *	@dev: network device
- *	@queue_index: sub queue index
- *
- * Resume individual transmit queue of a device with multiple transmit queues.
- */
-static inline void netif_wake_subqueue(struct net_device *dev, u16 queue_index)
-{
-	struct netdev_queue *txq = netdev_get_tx_queue(dev, queue_index);
-	if (test_and_clear_bit(__QUEUE_STATE_DRV_XOFF, &txq->state))
-		__netif_schedule(txq->qdisc);
-}
+void netif_wake_subqueue(struct net_device *dev, u16 queue_index);
 
 #ifdef CONFIG_XPS
 int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,

include/net/sch_generic.h

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index a3cfb8e..56838ab 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -259,7 +259,9 @@
 
 static inline struct Qdisc *qdisc_root(const struct Qdisc *qdisc)
 {
-	return qdisc->dev_queue->qdisc;
+	struct Qdisc *q = rcu_dereference_rtnl(qdisc->dev_queue->qdisc);
+
+	return q;
 }
 
 static inline struct Qdisc *qdisc_root_sleeping(const struct Qdisc *qdisc)
@@ -384,7 +386,7 @@
 	struct Qdisc *qdisc;
 
 	for (; i < dev->num_tx_queues; i++) {
-		qdisc = netdev_get_tx_queue(dev, i)->qdisc;
+		qdisc = rtnl_dereference(netdev_get_tx_queue(dev, i)->qdisc);
 		if (qdisc) {
 			spin_lock_bh(qdisc_lock(qdisc));
 			qdisc_reset(qdisc);
@@ -402,13 +404,18 @@
 static inline bool qdisc_all_tx_empty(const struct net_device *dev)
 {
 	unsigned int i;
+
+	rcu_read_lock();
 	for (i = 0; i < dev->num_tx_queues; i++) {
 		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
-		const struct Qdisc *q = txq->qdisc;
+		const struct Qdisc *q = rcu_dereference(txq->qdisc);
 
-		if (q->q.qlen)
+		if (q->q.qlen) {
+			rcu_read_unlock();
 			return false;
+		}
 	}
+	rcu_read_unlock();
 	return true;
 }
 
@@ -416,9 +423,10 @@
 static inline bool qdisc_tx_changing(const struct net_device *dev)
 {
 	unsigned int i;
+
 	for (i = 0; i < dev->num_tx_queues; i++) {
 		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
-		if (txq->qdisc != txq->qdisc_sleeping)
+		if (rcu_access_pointer(txq->qdisc) != txq->qdisc_sleeping)
 			return true;
 	}
 	return false;
@@ -428,9 +436,10 @@
 static inline bool qdisc_tx_is_noop(const struct net_device *dev)
 {
 	unsigned int i;
+
 	for (i = 0; i < dev->num_tx_queues; i++) {
 		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
-		if (txq->qdisc != &noop_qdisc)
+		if (rcu_access_pointer(txq->qdisc) != &noop_qdisc)
 			return false;
 	}
 	return true;