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>

2 files changed, 42 insertions, 1 deletions

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)