Re: PROBLEM: IProute hangs after running traffic shaping scripts

[Patrick McHardy <kaber@xxxxxxxxx>]

Szymon Miotk wrote:

> This mail was posted 02-11-2004 to linux-net@xxxxxxxxxxxxxxx, but I 
> got no response at all, so I am resending it.
>
> [1.] One line summary of the problem:
> IProute hangs after running traffic shaping scripts

Can you test if this patch helps please ? It immediately removes all
inner qdiscs of classful qdiscs from dev->qdisc_list, making it
impossible for anyone to look up an inner qdisc that is about to get
destroyed. Taking qdisc_tree_lock in qdisc_lookup is not really
necessary with this patch anymore, since all changes to dev->qdisc_list
happen under the rtnl again (which is also relied on for memory). I put
it in anyways for now until I have fully analyzed locking.

Regards
Patrick

===== net/sched/sch_api.c 1.42 vs edited =====
--- 1.42/net/sched/sch_api.c    2004-11-07 05:03:04 +01:00
+++ edited/net/sched/sch_api.c  2004-11-07 22:59:52 +01:00
@@ -194,13 +194,15 @@
 
 struct Qdisc *qdisc_lookup(struct net_device *dev, u32 handle)
 {
-       struct Qdisc *q;
+       struct Qdisc *q = NULL;
 
+       read_lock_bh(&qdisc_tree_lock);
        list_for_each_entry(q, &dev->qdisc_list, list) {
                if (q->handle == handle)
-                       return q;
+                       break;
        }
-       return NULL;
+       read_unlock_bh(&qdisc_tree_lock);
+       return q;
 }
 
 struct Qdisc *qdisc_leaf(struct Qdisc *p, u32 classid)
===== net/sched/sch_generic.c 1.30 vs edited =====
--- 1.30/net/sched/sch_generic.c        2004-11-06 01:34:45 +01:00
+++ edited/net/sched/sch_generic.c      2004-11-07 22:37:55 +01:00
@@ -483,10 +483,30 @@
 
 void qdisc_destroy(struct Qdisc *qdisc)
 {
+       struct list_head cql = LIST_HEAD_INIT(cql);
+       struct Qdisc *cq, *q, *n;
+
        if (qdisc->flags & TCQ_F_BUILTIN ||
                !atomic_dec_and_test(&qdisc->refcnt))
                return;
+
        list_del(&qdisc->list);
+
+       /* unlink inner qdiscs from dev->qdisc_list immediately */
+       if (qdisc->ops->cl_ops != NULL)
+               list_add(&qdisc->list, &cql);
+       list_for_each_entry(cq, &cql, list) {
+               list_for_each_entry_safe(q, n, &qdisc->dev->qdisc_list, list)
+               if (TC_H_MAJ(q->parent) == TC_H_MAJ(cq->handle)) {
+                       if (q->ops->cl_ops != NULL)
+                               list_move_tail(&q->list, &cql);
+                       else
+                               list_del_init(&q->list);
+               }
+       }
+       list_for_each_entry_safe(cq, n, &cql, list)
+               list_del_init(&cq->list);
+
        call_rcu(&qdisc->q_rcu, __qdisc_destroy);
 }