Re: [LARTC] [HTB] htb_dequeue_tree assertion (kernel 2.4.21-ac4)

[devik <devik@cdi.cz>]

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> > If you read comment above htb_dequeue_tree, it should be called
> > only when it is sure that there are packets inside of the level/prio.
> > It is known by other HTB mechanism (per-level activity lists).
> >
> > Thus the bugtrap is to catch case where class was inserted
> > into activity list because it had packets in its sub-qdisc
> > but when we actually decide to dequeue - it has no packet.
> > It is weird - can qdisc lose packets even when dequeue was
> > not called ??
>
> If you change the depth of the leave queue then it is possible to drop
> packets or if you completely exchange the queue. Which would also
> explain why the assertion only occurs when the configuration is altered.

Well, I agree that there is something wrong. Now it is neccessary to
find scenario where it does happen so that it is fixed in right way.
I have not much time these days to test these cases but your informations
would lead to following hypothesis:

Classe's child qdisc is replaced while old one still has nonzero queue.
New empty qdisc is grafted under class instead. What about attached
patch (it is against my latest version so you can see offset warnings) ?

devik

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--- sch_htb.c	2003/07/05 10:37:11	1.21
+++ sch_htb.c	2003/07/20 07:24:59
@@ -1286,6 +1286,10 @@ static int htb_graft(struct Qdisc *sch, 
 					return -ENOBUFS;
 		sch_tree_lock(sch);
 		if ((*old = xchg(&cl->un.leaf.q, new)) != NULL) {
+			/* TODO: test it */
+			if (cl->prio_activity)
+				htb_deactivate ((struct htb_sched*)sch->data,cl);
+
 			/* TODO: is it correct ? Why CBQ doesn't do it ? */
 			sch->q.qlen -= (*old)->q.qlen;	
 			qdisc_reset(*old);