pkt_sched: Fix qdisc list locking

Since some qdiscs call qdisc_tree_decrease_qlen() (so qdisc_lookup())
without rtnl_lock(), adding and deleting from a qdisc list needs
additional locking. This patch adds global spinlock qdisc_list_lock
and wrapper functions for modifying the list. It is considered as a
temporary solution until hfsc_dequeue(), netem_dequeue() and
tbf_dequeue() (or qdisc_tree_decrease_qlen()) are redone.

With feedback from Herbert Xu and David S. Miller.

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 853fe83..b786a5b 100644 (file)
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -78,6 +78,7 @@ extern struct Qdisc *fifo_create_dflt(struct Qdisc *sch, struct Qdisc_ops *ops,
 
 extern int register_qdisc(struct Qdisc_ops *qops);
 extern int unregister_qdisc(struct Qdisc_ops *qops);
+extern void qdisc_list_del(struct Qdisc *q);
 extern struct Qdisc *qdisc_lookup(struct net_device *dev, u32 handle);
 extern struct Qdisc *qdisc_lookup_class(struct net_device *dev, u32 handle);
 extern struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r,

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 45f442d..e7fb9e0 100644 (file)
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -199,19 +199,53 @@ struct Qdisc *qdisc_match_from_root(struct Qdisc *root, u32 handle)
        return NULL;
 }
 
+/*
+ * This lock is needed until some qdiscs stop calling qdisc_tree_decrease_qlen()
+ * without rtnl_lock(); currently hfsc_dequeue(), netem_dequeue(), tbf_dequeue()
+ */
+static DEFINE_SPINLOCK(qdisc_list_lock);
+
+static void qdisc_list_add(struct Qdisc *q)
+{
+       if ((q->parent != TC_H_ROOT) && !(q->flags & TCQ_F_INGRESS)) {
+               spin_lock_bh(&qdisc_list_lock);
+               list_add_tail(&q->list, &qdisc_root_sleeping(q)->list);
+               spin_unlock_bh(&qdisc_list_lock);
+       }
+}
+
+void qdisc_list_del(struct Qdisc *q)
+{
+       if ((q->parent != TC_H_ROOT) && !(q->flags & TCQ_F_INGRESS)) {
+               spin_lock_bh(&qdisc_list_lock);
+               list_del(&q->list);
+               spin_unlock_bh(&qdisc_list_lock);
+       }
+}
+EXPORT_SYMBOL(qdisc_list_del);
+
 struct Qdisc *qdisc_lookup(struct net_device *dev, u32 handle)
 {
        unsigned int i;
+       struct Qdisc *q;
+
+       spin_lock_bh(&qdisc_list_lock);
 
        for (i = 0; i < dev->num_tx_queues; i++) {
                struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
-               struct Qdisc *q, *txq_root = txq->qdisc_sleeping;
+               struct Qdisc *txq_root = txq->qdisc_sleeping;
 
                q = qdisc_match_from_root(txq_root, handle);
                if (q)
-                       return q;
+                       goto unlock;
        }
-       return qdisc_match_from_root(dev->rx_queue.qdisc_sleeping, handle);
+
+       q = qdisc_match_from_root(dev->rx_queue.qdisc_sleeping, handle);
+
+unlock:
+       spin_unlock_bh(&qdisc_list_lock);
+
+       return q;
 }
 
 static struct Qdisc *qdisc_leaf(struct Qdisc *p, u32 classid)
@@ -810,8 +844,8 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue,
                                goto err_out3;
                        }
                }
-               if ((parent != TC_H_ROOT) && !(sch->flags & TCQ_F_INGRESS))
-                       list_add_tail(&sch->list, &dev_queue->qdisc_sleeping->list);
+
+               qdisc_list_add(sch);
 
                return sch;
        }

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index c3ed4d4..5f0ade7 100644 (file)
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -526,10 +526,9 @@ void qdisc_destroy(struct Qdisc *qdisc)
            !atomic_dec_and_test(&qdisc->refcnt))
                return;
 
-       if (qdisc->parent)
-               list_del(&qdisc->list);
-
 #ifdef CONFIG_NET_SCHED
+       qdisc_list_del(qdisc);
+
        qdisc_put_stab(qdisc->stab);
 #endif
        gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);