pkt_sched: Manage qdisc list inside of root qdisc.

Idea is from Patrick McHardy.

Instead of managing the list of qdiscs on the device level, manage it
in the root qdisc of a netdev_queue.  This solves all kinds of
visibility issues during qdisc destruction.

The way to iterate over all qdiscs of a netdev_queue is to visit
the netdev_queue->qdisc, and then traverse it's list.

The only special case is to ignore builting qdiscs at the root when
dumping or doing a qdisc_lookup().  That was not needed previously
because builtin qdiscs were not added to the device's qdisc_list.

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 133 insertions, 52 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index b3ef8307204e..fb43731c9860 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -185,11 +185,20 @@ EXPORT_SYMBOL(unregister_qdisc);
 
 struct Qdisc *qdisc_lookup(struct net_device *dev, u32 handle)
 {
-        struct Qdisc *q;
+        unsigned int i;
+
+        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;
 
-        list_for_each_entry(q, &dev->qdisc_list, list) {
-                if (q->handle == handle)
-                        return q;
+                if (!(txq_root->flags & TCQ_F_BUILTIN) &&
+                    txq_root->handle == handle)
+                        return txq_root;
+
+                list_for_each_entry(q, &txq_root->list, list) {
+                        if (q->handle == handle)
+                                return q;
+                }
         }
         return NULL;
 }
@@ -676,9 +685,8 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue,
                                 goto err_out3;
                         }
                 }
-                spin_lock_bh(&dev->qdisc_list_lock);
-                list_add_tail(&sch->list, &dev->qdisc_list);
-                spin_unlock_bh(&dev->qdisc_list_lock);
+                if (parent)
+                        list_add_tail(&sch->list, &dev_queue->qdisc->list);
 
                 return sch;
         }
@@ -1037,13 +1045,57 @@ err_out:
         return -EINVAL;
 }
 
+static bool tc_qdisc_dump_ignore(struct Qdisc *q)
+{
+        return (q->flags & TCQ_F_BUILTIN) ? true : false;
+}
+
+static int tc_dump_qdisc_root(struct Qdisc *root, struct sk_buff *skb,
+                              struct netlink_callback *cb,
+                              int *q_idx_p, int s_q_idx)
+{
+        int ret = 0, q_idx = *q_idx_p;
+        struct Qdisc *q;
+
+        if (!root)
+                return 0;
+
+        q = root;
+        if (q_idx < s_q_idx) {
+                q_idx++;
+        } else {
+                if (!tc_qdisc_dump_ignore(q) &&
+                    tc_fill_qdisc(skb, q, q->parent, NETLINK_CB(cb->skb).pid,
+                                  cb->nlh->nlmsg_seq, NLM_F_MULTI, RTM_NEWQDISC) <= 0)
+                        goto done;
+                q_idx++;
+        }
+        list_for_each_entry(q, &root->list, list) {
+                if (q_idx < s_q_idx) {
+                        q_idx++;
+                        continue;
+                }
+                if (!tc_qdisc_dump_ignore(q) && 
+                    tc_fill_qdisc(skb, q, q->parent, NETLINK_CB(cb->skb).pid,
+                                  cb->nlh->nlmsg_seq, NLM_F_MULTI, RTM_NEWQDISC) <= 0)
+                        goto done;
+                q_idx++;
+        }
+
+out:
+        *q_idx_p = q_idx;
+        return ret;
+done:
+        ret = -1;
+        goto out;
+}
+
 static int tc_dump_qdisc(struct sk_buff *skb, struct netlink_callback *cb)
 {
         struct net *net = sock_net(skb->sk);
         int idx, q_idx;
         int s_idx, s_q_idx;
         struct net_device *dev;
-        struct Qdisc *q;
 
         if (net != &init_net)
                 return 0;
@@ -1053,21 +1105,22 @@ static int tc_dump_qdisc(struct sk_buff *skb, struct netlink_callback *cb)
         read_lock(&dev_base_lock);
         idx = 0;
         for_each_netdev(&init_net, dev) {
+                struct netdev_queue *dev_queue;
+
                 if (idx < s_idx)
                         goto cont;
                 if (idx > s_idx)
                         s_q_idx = 0;
                 q_idx = 0;
-                list_for_each_entry(q, &dev->qdisc_list, list) {
-                        if (q_idx < s_q_idx) {
-                                q_idx++;
-                                continue;
-                        }
-                        if (tc_fill_qdisc(skb, q, q->parent, NETLINK_CB(cb->skb).pid,
-                                          cb->nlh->nlmsg_seq, NLM_F_MULTI, RTM_NEWQDISC) <= 0)
-                                goto done;
-                        q_idx++;
-                }
+
+                dev_queue = netdev_get_tx_queue(dev, 0);
+                if (tc_dump_qdisc_root(dev_queue->qdisc, skb, cb, &q_idx, s_q_idx) < 0)
+                        goto done;
+
+                dev_queue = &dev->rx_queue;
+                if (tc_dump_qdisc_root(dev_queue->qdisc, skb, cb, &q_idx, s_q_idx) < 0)
+                        goto done;
+
 cont:
                 idx++;
         }
@@ -1285,15 +1338,62 @@ static int qdisc_class_dump(struct Qdisc *q, unsigned long cl, struct qdisc_walk
                               a->cb->nlh->nlmsg_seq, NLM_F_MULTI, RTM_NEWTCLASS);
 }
 
+static int tc_dump_tclass_qdisc(struct Qdisc *q, struct sk_buff *skb,
+                                struct tcmsg *tcm, struct netlink_callback *cb,
+                                int *t_p, int s_t)
+{
+        struct qdisc_dump_args arg;
+
+        if (tc_qdisc_dump_ignore(q) ||
+            *t_p < s_t || !q->ops->cl_ops ||
+            (tcm->tcm_parent &&
+             TC_H_MAJ(tcm->tcm_parent) != q->handle)) {
+                (*t_p)++;
+                return 0;
+        }
+        if (*t_p > s_t)
+                memset(&cb->args[1], 0, sizeof(cb->args)-sizeof(cb->args[0]));
+        arg.w.fn = qdisc_class_dump;
+        arg.skb = skb;
+        arg.cb = cb;
+        arg.w.stop  = 0;
+        arg.w.skip = cb->args[1];
+        arg.w.count = 0;
+        q->ops->cl_ops->walk(q, &arg.w);
+        cb->args[1] = arg.w.count;
+        if (arg.w.stop)
+                return -1;
+        (*t_p)++;
+        return 0;
+}
+
+static int tc_dump_tclass_root(struct Qdisc *root, struct sk_buff *skb,
+                               struct tcmsg *tcm, struct netlink_callback *cb,
+                               int *t_p, int s_t)
+{
+        struct Qdisc *q;
+
+        if (!root)
+                return 0;
+
+        if (tc_dump_tclass_qdisc(root, skb, tcm, cb, t_p, s_t) < 0)
+                return -1;
+
+        list_for_each_entry(q, &root->list, list) {
+                if (tc_dump_tclass_qdisc(q, skb, tcm, cb, t_p, s_t) < 0)
+                        return -1;
+        }
+
+        return 0;
+}
+
 static int tc_dump_tclass(struct sk_buff *skb, struct netlink_callback *cb)
 {
+        struct tcmsg *tcm = (struct tcmsg*)NLMSG_DATA(cb->nlh);
         struct net *net = sock_net(skb->sk);
-        int t;
-        int s_t;
+        struct netdev_queue *dev_queue;
         struct net_device *dev;
-        struct Qdisc *q;
-        struct tcmsg *tcm = (struct tcmsg*)NLMSG_DATA(cb->nlh);
-        struct qdisc_dump_args arg;
+        int t, s_t;
 
         if (net != &init_net)
                 return 0;
@@ -1306,28 +1406,15 @@ static int tc_dump_tclass(struct sk_buff *skb, struct netlink_callback *cb)
         s_t = cb->args[0];
         t = 0;
 
-        list_for_each_entry(q, &dev->qdisc_list, list) {
-                if (t < s_t || !q->ops->cl_ops ||
-                    (tcm->tcm_parent &&
-                     TC_H_MAJ(tcm->tcm_parent) != q->handle)) {
-                        t++;
-                        continue;
-                }
-                if (t > s_t)
-                        memset(&cb->args[1], 0, sizeof(cb->args)-sizeof(cb->args[0]));
-                arg.w.fn = qdisc_class_dump;
-                arg.skb = skb;
-                arg.cb = cb;
-                arg.w.stop  = 0;
-                arg.w.skip = cb->args[1];
-                arg.w.count = 0;
-                q->ops->cl_ops->walk(q, &arg.w);
-                cb->args[1] = arg.w.count;
-                if (arg.w.stop)
-                        break;
-                t++;
-        }
+        dev_queue = netdev_get_tx_queue(dev, 0);
+        if (tc_dump_tclass_root(dev_queue->qdisc, skb, tcm, cb, &t, s_t) < 0)
+                goto done;
+
+        dev_queue = &dev->rx_queue;
+        if (tc_dump_tclass_root(dev_queue->qdisc, skb, tcm, cb, &t, s_t) < 0)
+                goto done;
 
+done:
         cb->args[0] = t;
 
         dev_put(dev);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index e244c462e6bd..14cc443d0490 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -480,15 +480,12 @@ static void __qdisc_destroy(struct rcu_head *head)
 
 void qdisc_destroy(struct Qdisc *qdisc)
 {
-        struct net_device *dev = qdisc_dev(qdisc);
-
         if (qdisc->flags & TCQ_F_BUILTIN ||
             !atomic_dec_and_test(&qdisc->refcnt))
                 return;
 
-        spin_lock_bh(&dev->qdisc_list_lock);
-        list_del(&qdisc->list);
-        spin_unlock_bh(&dev->qdisc_list_lock);
+        if (qdisc->parent)
+                list_del(&qdisc->list);
 
         call_rcu(&qdisc->q_rcu, __qdisc_destroy);
 }
@@ -520,9 +517,6 @@ static void attach_one_default_qdisc(struct net_device *dev,
                         printk(KERN_INFO "%s: activation failed\n", dev->name);
                         return;
                 }
-                spin_lock_bh(&dev->qdisc_list_lock);
-                list_add_tail(&qdisc->list, &dev->qdisc_list);
-                spin_unlock_bh(&dev->qdisc_list_lock);
         } else {
                 qdisc =  &noqueue_qdisc;
         }