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>

3 files changed, 42 insertions, 8 deletions

diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 853fe83d9f37..b786a5b09253 100644
--- 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 45f442d7de47..e7fb9e0d21b4 100644
--- 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 c3ed4d44fc14..5f0ade7806a7 100644
--- 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);