net: sched: extend Qdisc with rcu

Currently, Qdisc API functions assume that users have rtnl lock taken. To
implement rtnl unlocked classifiers update interface, Qdisc API must be
extended with functions that do not require rtnl lock.

Extend Qdisc structure with rcu. Implement special version of put function
qdisc_put_unlocked() that is called without rtnl lock taken. This function
only takes rtnl lock if Qdisc reference counter reached zero and is
intended to be used as optimization.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 50 insertions, 1 deletions

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 9cdd76348d9a..bb9cb84114c1 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -85,6 +85,11 @@ static inline struct netdev_queue *dev_ingress_queue(struct net_device *dev)
 	return rtnl_dereference(dev->ingress_queue);
 }
 
+static inline struct netdev_queue *dev_ingress_queue_rcu(struct net_device *dev)
+{
+	return rcu_dereference(dev->ingress_queue);
+}
+
 struct netdev_queue *dev_ingress_queue_create(struct net_device *dev);
 
 #ifdef CONFIG_NET_INGRESS
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 7dc769e5452b..a16fbe9a2a67 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -102,6 +102,7 @@ int qdisc_set_default(const char *id);
 void qdisc_hash_add(struct Qdisc *q, bool invisible);
 void qdisc_hash_del(struct Qdisc *q);
 struct Qdisc *qdisc_lookup(struct net_device *dev, u32 handle);
+struct Qdisc *qdisc_lookup_rcu(struct net_device *dev, u32 handle);
 struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r,
 					struct nlattr *tab,
 					struct netlink_ext_ack *extack);
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index fadb1a4d4ee8..091b40c198ff 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -105,6 +105,7 @@ struct Qdisc {
 
 	spinlock_t		busylock ____cacheline_aligned_in_smp;
 	spinlock_t		seqlock;
+	struct rcu_head		rcu;
 };
 
 static inline void qdisc_refcount_inc(struct Qdisc *qdisc)
@@ -555,6 +556,7 @@ struct Qdisc *dev_graft_qdisc(struct netdev_queue *dev_queue,
 			      struct Qdisc *qdisc);
 void qdisc_reset(struct Qdisc *qdisc);
 void qdisc_put(struct Qdisc *qdisc);
+void qdisc_put_unlocked(struct Qdisc *qdisc);
 void qdisc_tree_reduce_backlog(struct Qdisc *qdisc, unsigned int n,
 			       unsigned int len);
 struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 2096138c4bf6..22e9799e5b69 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -314,6 +314,24 @@ out:
 	return q;
 }
 
+struct Qdisc *qdisc_lookup_rcu(struct net_device *dev, u32 handle)
+{
+	struct netdev_queue *nq;
+	struct Qdisc *q;
+
+	if (!handle)
+		return NULL;
+	q = qdisc_match_from_root(dev->qdisc, handle);
+	if (q)
+		goto out;
+
+	nq = dev_ingress_queue_rcu(dev);
+	if (nq)
+		q = qdisc_match_from_root(nq->qdisc_sleeping, handle);
+out:
+	return q;
+}
+
 static struct Qdisc *qdisc_leaf(struct Qdisc *p, u32 classid)
 {
 	unsigned long cl;
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 3e7696f3e053..531fac1d2875 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -941,6 +941,13 @@ void qdisc_free(struct Qdisc *qdisc)
 	kfree((char *) qdisc - qdisc->padded);
 }
 
+void qdisc_free_cb(struct rcu_head *head)
+{
+	struct Qdisc *q = container_of(head, struct Qdisc, rcu);
+
+	qdisc_free(q);
+}
+
 static void qdisc_destroy(struct Qdisc *qdisc)
 {
 	const struct Qdisc_ops  *ops = qdisc->ops;
@@ -970,7 +977,7 @@ static void qdisc_destroy(struct Qdisc *qdisc)
 		kfree_skb_list(skb);
 	}
 
-	qdisc_free(qdisc);
+	call_rcu(&qdisc->rcu, qdisc_free_cb);
 }
 
 void qdisc_put(struct Qdisc *qdisc)
@@ -983,6 +990,22 @@ void qdisc_put(struct Qdisc *qdisc)
 }
 EXPORT_SYMBOL(qdisc_put);
 
+/* Version of qdisc_put() that is called with rtnl mutex unlocked.
+ * Intended to be used as optimization, this function only takes rtnl lock if
+ * qdisc reference counter reached zero.
+ */
+
+void qdisc_put_unlocked(struct Qdisc *qdisc)
+{
+	if (qdisc->flags & TCQ_F_BUILTIN ||
+	    !refcount_dec_and_rtnl_lock(&qdisc->refcnt))
+		return;
+
+	qdisc_destroy(qdisc);
+	rtnl_unlock();
+}
+EXPORT_SYMBOL(qdisc_put_unlocked);
+
 /* Attach toplevel qdisc to device queue. */
 struct Qdisc *dev_graft_qdisc(struct netdev_queue *dev_queue,
 			      struct Qdisc *qdisc)