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>

3 files changed, 14 insertions, 9 deletions

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 19696ebe9ebc..346ef85617d3 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -783,7 +783,7 @@ static void dev_deactivate_queue(struct net_device *dev,
 	struct Qdisc *qdisc_default = _qdisc_default;
 	struct Qdisc *qdisc;
 
-	qdisc = dev_queue->qdisc;
+	qdisc = rtnl_dereference(dev_queue->qdisc);
 	if (qdisc) {
 		spin_lock_bh(qdisc_lock(qdisc));
 
@@ -876,7 +876,7 @@ static void dev_init_scheduler_queue(struct net_device *dev,
 {
 	struct Qdisc *qdisc = _qdisc;
 
-	dev_queue->qdisc = qdisc;
+	rcu_assign_pointer(dev_queue->qdisc, qdisc);
 	dev_queue->qdisc_sleeping = qdisc;
 }
 
diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
index 6749e2f540d0..37e7d25d21f1 100644
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -231,7 +231,7 @@ static int mqprio_dump(struct Qdisc *sch, struct sk_buff *skb)
 	memset(&sch->qstats, 0, sizeof(sch->qstats));
 
 	for (i = 0; i < dev->num_tx_queues; i++) {
-		qdisc = netdev_get_tx_queue(dev, i)->qdisc;
+		qdisc = rtnl_dereference(netdev_get_tx_queue(dev, i)->qdisc);
 		spin_lock_bh(qdisc_lock(qdisc));
 		sch->q.qlen		+= qdisc->q.qlen;
 		sch->bstats.bytes	+= qdisc->bstats.bytes;
@@ -340,7 +340,9 @@ static int mqprio_dump_class_stats(struct Qdisc *sch, unsigned long cl,
 		spin_unlock_bh(d->lock);
 
 		for (i = tc.offset; i < tc.offset + tc.count; i++) {
-			qdisc = netdev_get_tx_queue(dev, i)->qdisc;
+			struct netdev_queue *q = netdev_get_tx_queue(dev, i);
+
+			qdisc = rtnl_dereference(q->qdisc);
 			spin_lock_bh(qdisc_lock(qdisc));
 			bstats.bytes      += qdisc->bstats.bytes;
 			bstats.packets    += qdisc->bstats.packets;
diff --git a/net/sched/sch_teql.c b/net/sched/sch_teql.c
index aaa8d03ed054..5cd291bd00e4 100644
--- a/net/sched/sch_teql.c
+++ b/net/sched/sch_teql.c
@@ -96,11 +96,14 @@ teql_dequeue(struct Qdisc *sch)
 	struct teql_sched_data *dat = qdisc_priv(sch);
 	struct netdev_queue *dat_queue;
 	struct sk_buff *skb;
+	struct Qdisc *q;
 
 	skb = __skb_dequeue(&dat->q);
 	dat_queue = netdev_get_tx_queue(dat->m->dev, 0);
+	q = rcu_dereference_bh(dat_queue->qdisc);
+
 	if (skb == NULL) {
-		struct net_device *m = qdisc_dev(dat_queue->qdisc);
+		struct net_device *m = qdisc_dev(q);
 		if (m) {
 			dat->m->slaves = sch;
 			netif_wake_queue(m);
@@ -108,7 +111,7 @@ teql_dequeue(struct Qdisc *sch)
 	} else {
 		qdisc_bstats_update(sch, skb);
 	}
-	sch->q.qlen = dat->q.qlen + dat_queue->qdisc->q.qlen;
+	sch->q.qlen = dat->q.qlen + q->q.qlen;
 	return skb;
 }
 
@@ -157,9 +160,9 @@ teql_destroy(struct Qdisc *sch)
 						txq = netdev_get_tx_queue(master->dev, 0);
 						master->slaves = NULL;
 
-						root_lock = qdisc_root_sleeping_lock(txq->qdisc);
+						root_lock = qdisc_root_sleeping_lock(rtnl_dereference(txq->qdisc));
 						spin_lock_bh(root_lock);
-						qdisc_reset(txq->qdisc);
+						qdisc_reset(rtnl_dereference(txq->qdisc));
 						spin_unlock_bh(root_lock);
 					}
 				}
@@ -266,7 +269,7 @@ static inline int teql_resolve(struct sk_buff *skb,
 	struct dst_entry *dst = skb_dst(skb);
 	int res;
 
-	if (txq->qdisc == &noop_qdisc)
+	if (rcu_access_pointer(txq->qdisc) == &noop_qdisc)
 		return -ENODEV;
 
 	if (!dev->header_ops || !dst)