Merge branch 'ets-use-old-nbands-while-purging-unused-classes'

Davide Caratti says:

====================
ets: use old 'nbands' while purging unused classes

- patch 1/2 fixes a NULL dereference in the control path of sch_ets qdisc
- patch 2/2 extends kselftests to verify effectiveness of the above fix
====================

Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

net/sched/sch_ets.c

@@ -651,18 +651,19 @@ static int ets_qdisc_change(struct Qdisc *sch, struct nlattr *opt,
 
 	sch_tree_lock(sch);
 
+	for (i = nbands; i < oldbands; i++) {
+		if (i >= q->nstrict && q->classes[i].qdisc->q.qlen)
+			list_del_init(&q->classes[i].alist);
+		qdisc_purge_queue(q->classes[i].qdisc);
+	}
+
 	WRITE_ONCE(q->nbands, nbands);
 	for (i = nstrict; i < q->nstrict; i++) {
 		if (q->classes[i].qdisc->q.qlen) {
 			list_add_tail(&q->classes[i].alist, &q->active);
 			q->classes[i].deficit = quanta[i];
 		}
 	}
-	for (i = q->nbands; i < oldbands; i++) {
-		if (i >= q->nstrict && q->classes[i].qdisc->q.qlen)
-			list_del_init(&q->classes[i].alist);
-		qdisc_purge_queue(q->classes[i].qdisc);
-	}
 	WRITE_ONCE(q->nstrict, nstrict);
 	memcpy(q->prio2band, priomap, sizeof(priomap));
 

tools/testing/selftests/net/forwarding/sch_ets.sh

@@ -11,6 +11,7 @@ ALL_TESTS="
 	ets_test_strict
 	ets_test_mixed
 	ets_test_dwrr
+	ets_test_plug
 	classifier_mode
 	ets_test_strict
 	ets_test_mixed

tools/testing/selftests/net/forwarding/sch_ets_tests.sh

@@ -224,3 +224,11 @@ ets_test_dwrr()
 	ets_set_dwrr_two_bands
 	xfail_on_slow ets_dwrr_test_01
 }
+
+ets_test_plug()
+{
+	ets_change_qdisc $put 2 "3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3" "1514 1514"
+	tc qdisc add dev $put handle 20: parent 10:4 plug
+	start_traffic_pktsize 100 $h1.10 192.0.2.1 192.0.2.2 00:c1:a0:c1:a0:00 "-c 1"
+	ets_qdisc_setup $put 2
+}