pkt_sched: Add and use qdisc_root() and qdisc_root_lock().

When code wants to lock the qdisc tree state, the logic
operation it's doing is locking the top-level qdisc that
sits of the root of the netdev_queue.

Add qdisc_root_lock() to represent this and convert the
easiest cases.

In order for this to work out in all cases, we have to
hook up the noop_qdisc to a dummy netdev_queue.

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

1 files changed, 16 insertions, 5 deletions

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index ac208c2b2d10..739a8711ab30 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -151,14 +151,17 @@ static inline int qdisc_restart(struct netdev_queue *txq,
 {
         int ret = NETDEV_TX_BUSY;
         struct net_device *dev;
+        spinlock_t *root_lock;
         struct sk_buff *skb;
 
         /* Dequeue packet */
         if (unlikely((skb = dequeue_skb(q)) == NULL))
                 return 0;
 
-        /* And release queue */
-        spin_unlock(&txq->lock);
+        root_lock = qdisc_root_lock(q);
+
+        /* And release qdisc */
+        spin_unlock(root_lock);
 
         dev = txq->dev;
 
@@ -167,7 +170,7 @@ static inline int qdisc_restart(struct netdev_queue *txq,
                 ret = dev_hard_start_xmit(skb, dev, txq);
         HARD_TX_UNLOCK(dev, txq);
 
-        spin_lock(&txq->lock);
+        spin_lock(root_lock);
 
         switch (ret) {
         case NETDEV_TX_OK:
@@ -345,12 +348,18 @@ struct Qdisc_ops noop_qdisc_ops __read_mostly = {
         .owner          =       THIS_MODULE,
 };
 
+static struct netdev_queue noop_netdev_queue = {
+        .lock           =       __SPIN_LOCK_UNLOCKED(noop_netdev_queue.lock),
+        .qdisc          =       &noop_qdisc,
+};
+
 struct Qdisc noop_qdisc = {
         .enqueue        =       noop_enqueue,
         .dequeue        =       noop_dequeue,
         .flags          =       TCQ_F_BUILTIN,
         .ops            =       &noop_qdisc_ops,
         .list           =       LIST_HEAD_INIT(noop_qdisc.list),
+        .dev_queue      =       &noop_netdev_queue,
 };
 EXPORT_SYMBOL(noop_qdisc);
 
@@ -666,19 +675,21 @@ static bool some_qdisc_is_running(struct net_device *dev, int lock)
 
         for (i = 0; i < dev->num_tx_queues; i++) {
                 struct netdev_queue *dev_queue;
+                spinlock_t *root_lock;
                 struct Qdisc *q;
                 int val;
 
                 dev_queue = netdev_get_tx_queue(dev, i);
                 q = dev_queue->qdisc;
+                root_lock = qdisc_root_lock(q);
 
                 if (lock)
-                        spin_lock_bh(&dev_queue->lock);
+                        spin_lock_bh(root_lock);
 
                 val = test_bit(__QDISC_STATE_RUNNING, &q->state);
 
                 if (lock)
-                        spin_unlock_bh(&dev_queue->lock);
+                        spin_unlock_bh(root_lock);
 
                 if (val)
                         return true;