[PATCH 2.6] CBQ: Destroy filters before destroying classes

[PATCH 2.6] CBQ: Destroy filters before destroying classes

[Thomas Graf]

Dave,

CBQ destroys its classes by traversing the hashtable and thus classes
are not destroyed from root to leafs which means that class Y being
a subclass of class X may be destroyed before X. This is a problem
if a filter is attached to class X (parent) classifying into class Y
(result). In case Y gets deleted before X the filter references an
already deleted class while trying to unbind (cbq_unbind_filter).
Therefore all filters must be destroyed before destroying classes. An
additional BUG_TRAP has been added to document this not so obvious case.

Patch is relative to  "Convert Qdiscs to use generic network
statistics/estimator" patchset.

Signed-off-by: Thomas Graf <tgraf@suug.ch>

The BUG can be triggered with the following commands:
$TC qdisc add dev $DEV root handle 10:0 cbq bandwidth 100Mbit avpkt 1400 mpu 64
$TC class add dev $DEV parent 10:0  classid 10:12 cbq bandwidth 100mbit \
       rate 100mbit allot 1514 prio 3 maxburst 1 avpkt  500 bounded
$TC class add dev $DEV parent 10:12  classid 10:13 cbq bandwidth 100mbit \
       rate 100mbit allot 1514 prio 3 maxburst 1 avpkt  500 bounded
$TC filter add dev $DEV parent 10:12 protocol ip prio 10 u32 match ip protocol 6 0xff flowid 10:13
$TC qdisc del dev $DEV root

The deletion ordering in the above case is: 10:0 -> 10:13 -> 10:12

diff -Nru linux-2.6.9-rc3-bk6.orig/net/sched/sch_cbq.c linux-2.6.9-rc3-bk6/net/sched/sch_cbq.c
--- linux-2.6.9-rc3-bk6.orig/net/sched/sch_cbq.c	2004-10-07 00:32:25.000000000 +0200
+++ linux-2.6.9-rc3-bk6/net/sched/sch_cbq.c	2004-10-07 18:44:44.000000000 +0200
@@ -1749,6 +1749,8 @@
 {
 	struct cbq_sched_data *q = qdisc_priv(sch);
 
+	BUG_TRAP(!cl->filters);
+
 	cbq_destroy_filters(cl);
 	qdisc_destroy(cl->q);
 	qdisc_put_rtab(cl->R_tab);
@@ -1769,6 +1771,14 @@
 #ifdef CONFIG_NET_CLS_POLICE
 	q->rx_class = NULL;
 #endif
+	/*
+	 * Filters must be destroyed first because we don't destroy the
+	 * classes from root to leafs which means that filters can still
+	 * be bound to classes which have been destroyed already. --TGR '04
+	 */
+	for (h = 0; h < 16; h++)
+		for (cl = q->classes[h]; cl; cl = cl->next)
+			cbq_destroy_filters(cl);
 
 	for (h = 0; h < 16; h++) {
 		struct cbq_class *next;

Re: [PATCH 2.6] CBQ: Destroy filters before destroying classes

[David S. Miller]

On Thu, 7 Oct 2004 19:53:13 +0200
Thomas Graf <tgraf@suug.ch> wrote:

> CBQ destroys its classes by traversing the hashtable and thus classes
> are not destroyed from root to leafs which means that class Y being
> a subclass of class X may be destroyed before X. This is a problem
> if a filter is attached to class X (parent) classifying into class Y
> (result). In case Y gets deleted before X the filter references an
> already deleted class while trying to unbind (cbq_unbind_filter).
> Therefore all filters must be destroyed before destroying classes. An
> additional BUG_TRAP has been added to document this not so obvious case.

Applied, thanks a lot Thomas.

> Patch is relative to  "Convert Qdiscs to use generic network
> statistics/estimator" patchset.

BTW, that patch set forgot to handle sch_atm.c, I'm beginning to
believe that I'm the only developer with this packet scheduler
enabled in his test builds :-)  Most people don't have it enabled
because it requires CONFIG_ATM to be on.

Anyways, I fixed that up as follows.

# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
#   2004/10/19 21:11:02-07:00 davem@nuts.davemloft.net 
#   [PKT_SCHED]: Fix sch_atm build.
#   
#   Move it over to use qstats/bstats.
#   
#   Signed-off-by: David S. Miller <davem@davemloft.net>
# 
# net/sched/sch_atm.c
#   2004/10/19 21:10:26-07:00 davem@nuts.davemloft.net +4 -4
#   [PKT_SCHED]: Fix sch_atm build.
# 
diff -Nru a/net/sched/sch_atm.c b/net/sched/sch_atm.c
--- a/net/sched/sch_atm.c	2004-10-19 21:21:59 -07:00
+++ b/net/sched/sch_atm.c	2004-10-19 21:21:59 -07:00
@@ -449,12 +449,12 @@
 	    result == TC_POLICE_SHOT ||
 #endif
 	    (ret = flow->q->enqueue(skb,flow->q)) != 0) {
-		sch->stats.drops++;
+		sch->qstats.drops++;
 		if (flow) flow->stats.drops++;
 		return ret;
 	}
-	sch->stats.bytes += skb->len;
-	sch->stats.packets++;
+	sch->bstats.bytes += skb->len;
+	sch->bstats.packets++;
 	flow->stats.bytes += skb->len;
 	flow->stats.packets++;
 	/*
@@ -547,7 +547,7 @@
 	ret = p->link.q->ops->requeue(skb,p->link.q);
 	if (!ret) sch->q.qlen++;
 	else {
-		sch->stats.drops++;
+		sch->qstats.drops++;
 		p->link.stats.drops++;
 	}
 	return ret;

Re: [PATCH 2.6] CBQ: Destroy filters before destroying classes

[Thomas Graf]

* David S. Miller <20041019213906.2aced91d.davem@davemloft.net> 2004-10-19 21:39
> BTW, that patch set forgot to handle sch_atm.c, I'm beginning to
> believe that I'm the only developer with this packet scheduler
> enabled in his test builds :-)  Most people don't have it enabled
> because it requires CONFIG_ATM to be on.

My apologies and thanks for fixing it. I have put it on now :->
I will submit patches to convert the class part of classful qdiscs
later today.