net: sched: drop qdisc_reset from dev_graft_qdisc

In qdisc_graft_qdisc a "new" qdisc is attached and the 'qdisc_destroy'
operation is called on the old qdisc. The destroy operation will wait
a rcu grace period and call qdisc_rcu_free(). At which point
gso_cpu_skb is free'd along with all stats so no need to zero stats
and gso_cpu_skb from the graft operation itself.

Further after dropping the qdisc locks we can not continue to call
qdisc_reset before waiting an rcu grace period so that the qdisc is
detached from all cpus. By removing the qdisc_reset() here we get
the correct property of waiting an rcu grace period and letting the
qdisc_destroy operation clean up the qdisc correctly.

Note, a refcnt greater than 1 would cause the destroy operation to
be aborted however if this ever happened the reference to the qdisc
would be lost and we would have a memory leak.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index dfeabe319c566f55b720bab429d4173b26bff9b6..482ba2234470732167f57356a9d192ff52ea9e5b 100644 (file)
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -819,10 +819,6 @@ struct Qdisc *dev_graft_qdisc(struct netdev_queue *dev_queue,
        root_lock = qdisc_lock(oqdisc);
        spin_lock_bh(root_lock);
 
-       /* Prune old scheduler */
-       if (oqdisc && refcount_read(&oqdisc->refcnt) <= 1)
-               qdisc_reset(oqdisc);
-
        /* ... and graft new one */
        if (qdisc == NULL)
                qdisc = &noop_qdisc;
@@ -977,6 +973,16 @@ static bool some_qdisc_is_busy(struct net_device *dev)
        return false;
 }
 
+static void dev_qdisc_reset(struct net_device *dev,
+                           struct netdev_queue *dev_queue,
+                           void *none)
+{
+       struct Qdisc *qdisc = dev_queue->qdisc_sleeping;
+
+       if (qdisc)
+               qdisc_reset(qdisc);
+}
+
 /**
  *     dev_deactivate_many - deactivate transmissions on several devices
  *     @head: list of devices to deactivate
@@ -987,7 +993,6 @@ static bool some_qdisc_is_busy(struct net_device *dev)
 void dev_deactivate_many(struct list_head *head)
 {
        struct net_device *dev;
-       bool sync_needed = false;
 
        list_for_each_entry(dev, head, close_list) {
                netdev_for_each_tx_queue(dev, dev_deactivate_queue,
@@ -997,20 +1002,25 @@ void dev_deactivate_many(struct list_head *head)
                                             &noop_qdisc);
 
                dev_watchdog_down(dev);
-               sync_needed |= !dev->dismantle;
        }
 
        /* Wait for outstanding qdisc-less dev_queue_xmit calls.
         * This is avoided if all devices are in dismantle phase :
         * Caller will call synchronize_net() for us
         */
-       if (sync_needed)
-               synchronize_net();
+       synchronize_net();
 
        /* Wait for outstanding qdisc_run calls. */
-       list_for_each_entry(dev, head, close_list)
+       list_for_each_entry(dev, head, close_list) {
                while (some_qdisc_is_busy(dev))
                        yield();
+               /* The new qdisc is assigned at this point so we can safely
+                * unwind stale skb lists and qdisc statistics
+                */
+               netdev_for_each_tx_queue(dev, dev_qdisc_reset, NULL);
+               if (dev_ingress_queue(dev))
+                       dev_qdisc_reset(dev, dev_ingress_queue(dev), NULL);
+       }
 }
 
 void dev_deactivate(struct net_device *dev)