[NET_SCHED]: Eliminate qdisc_tree_lock

Since we're now holding the rtnl during the entire dump operation, we
can remove qdisc_tree_lock, whose only purpose is to protect dump
callbacks from concurrent changes to the qdisc tree.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 22 deletions

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 52eb3439d7c6..1894eb72f6cf 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -36,34 +36,23 @@
 
 /* Main transmission queue. */
 
-/* Main qdisc structure lock.
-
-   However, modifications
-   to data, participating in scheduling must be additionally
-   protected with dev->queue_lock spinlock.
-
-   The idea is the following:
-   - enqueue, dequeue are serialized via top level device
-     spinlock dev->queue_lock.
-   - tree walking is protected by read_lock(qdisc_tree_lock)
-     and this lock is used only in process context.
-   - updates to tree are made only under rtnl semaphore,
-     hence this lock may be made without local bh disabling.
-
-   qdisc_tree_lock must be grabbed BEFORE dev->queue_lock!
+/* Modifications to data participating in scheduling must be protected with
+ * dev->queue_lock spinlock.
+ *
+ * The idea is the following:
+ * - enqueue, dequeue are serialized via top level device
+ *   spinlock dev->queue_lock.
+ * - updates to tree and tree walking are only done under the rtnl mutex.
  */
-DEFINE_RWLOCK(qdisc_tree_lock);
 
 void qdisc_lock_tree(struct net_device *dev)
 {
-        write_lock(&qdisc_tree_lock);
         spin_lock_bh(&dev->queue_lock);
 }
 
 void qdisc_unlock_tree(struct net_device *dev)
 {
         spin_unlock_bh(&dev->queue_lock);
-        write_unlock(&qdisc_tree_lock);
 }
 
 /*
@@ -528,15 +517,11 @@ void dev_activate(struct net_device *dev)
                                 printk(KERN_INFO "%s: activation failed\n", dev->name);
                                 return;
                         }
-                        write_lock(&qdisc_tree_lock);
                         list_add_tail(&qdisc->list, &dev->qdisc_list);
-                        write_unlock(&qdisc_tree_lock);
                 } else {
                         qdisc =  &noqueue_qdisc;
                 }
-                write_lock(&qdisc_tree_lock);
                 dev->qdisc_sleeping = qdisc;
-                write_unlock(&qdisc_tree_lock);
         }
 
         if (!netif_carrier_ok(dev))