pkt_sched: Don't hold qdisc lock over qdisc_destroy().

Based upon reports by Denys Fedoryshchenko, and feedback
and help from Jarek Poplawski and Herbert Xu.

We always either:

1) Never made an external reference to this qdisc.

or

2) Did a dev_deactivate() which purged all asynchronous
   references.

So do not lock the qdisc when we call qdisc_destroy(),
it's illegal anyways as when we drop the lock this is
free'd memory.

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

2 files changed, 2 insertions, 17 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 7d7070b1eebd..d91a2338877c 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -638,11 +638,8 @@ static void notify_and_destroy(struct sk_buff *skb, struct nlmsghdr *n, u32 clid
         if (new || old)
                 qdisc_notify(skb, n, clid, old, new);
 
-        if (old) {
-                sch_tree_lock(old);
+        if (old)
                 qdisc_destroy(old);
-                sch_tree_unlock(old);
-        }
 }
 
 /* Graft qdisc "new" to class "classid" of qdisc "parent" or
@@ -1092,16 +1089,10 @@ create_n_graft:
 
 graft:
         if (1) {
-                spinlock_t *root_lock;
-
                 err = qdisc_graft(dev, p, skb, n, clid, q, NULL);
                 if (err) {
-                        if (q) {
-                                root_lock = qdisc_root_lock(q);
-                                spin_lock_bh(root_lock);
+                        if (q)
                                 qdisc_destroy(q);
-                                spin_unlock_bh(root_lock);
-                        }
                         return err;
                 }
         }
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 6f96b7bc0809..c3ed4d44fc14 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -518,8 +518,6 @@ void qdisc_reset(struct Qdisc *qdisc)
 }
 EXPORT_SYMBOL(qdisc_reset);
 
-/* Under qdisc_lock(qdisc) and BH! */
-
 void qdisc_destroy(struct Qdisc *qdisc)
 {
         const struct Qdisc_ops  *ops = qdisc->ops;
@@ -712,14 +710,10 @@ static void shutdown_scheduler_queue(struct net_device *dev,
         struct Qdisc *qdisc_default = _qdisc_default;
 
         if (qdisc) {
-                spinlock_t *root_lock = qdisc_lock(qdisc);
-
                 dev_queue->qdisc = qdisc_default;
                 dev_queue->qdisc_sleeping = qdisc_default;
 
-                spin_lock_bh(root_lock);
                 qdisc_destroy(qdisc);
-                spin_unlock_bh(root_lock);
         }
 }