[PATCH net-next] net/sched: sch_ets: properly init all active DRR list handles

leaf classes of ETS qdiscs are served in strict priority or deficit round
robin (DRR), depending on the value of 'nstrict'. Since this value can be
changed while traffic is running, we need to be sure that the active list
of DRR classes can be updated at any time, so:

1) call INIT_LIST_HEAD(&alist) on all leaf classes in .init(), before the
   first packet hits any of them.
2) ensure that 'alist' is not overwritten with zeros when a leaf class is
   no more strict priority nor DRR (i.e. array elements beyond 'nbands').

Link: https://lore.kernel.org/netdev/YS%2FoZ+f0Nr8eQkzH@dcaratti.users.ipa.redhat.com
Suggested-by: Cong Wang <redacted>
Signed-off-by: Davide Caratti <redacted>
---
 net/sched/sch_ets.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_ets.c b/net/sched/sch_ets.c
index 1f857ffd1ac2..ed86b7021f6d 100644
--- a/net/sched/sch_ets.c
+++ b/net/sched/sch_ets.c

@@ -661,7 +661,6 @@ static int ets_qdisc_change(struct Qdisc *sch, struct nlattr *opt,
 
 	q->nbands = nbands;
 	for (i = nstrict; i < q->nstrict; i++) {
-		INIT_LIST_HEAD(&q->classes[i].alist);
 		if (q->classes[i].qdisc->q.qlen) {
 			list_add_tail(&q->classes[i].alist, &q->active);
 			q->classes[i].deficit = quanta[i];

@@ -687,7 +686,11 @@ static int ets_qdisc_change(struct Qdisc *sch, struct nlattr *opt,
 	ets_offload_change(sch);
 	for (i = q->nbands; i < oldbands; i++) {
 		qdisc_put(q->classes[i].qdisc);
-		memset(&q->classes[i], 0, sizeof(q->classes[i]));
+		q->classes[i].qdisc = NULL;
+		q->classes[i].quantum = 0;
+		q->classes[i].deficit = 0;
+		memset(&q->classes[i].bstats, 0, sizeof(q->classes[i].bstats));
+		memset(&q->classes[i].qstats, 0, sizeof(q->classes[i].qstats));
 	}
 	return 0;
 }

@@ -696,7 +699,7 @@ static int ets_qdisc_init(struct Qdisc *sch, struct nlattr *opt,
 			  struct netlink_ext_ack *extack)
 {
 	struct ets_sched *q = qdisc_priv(sch);
-	int err;
+	int err, i;
 
 	if (!opt)
 		return -EINVAL;

@@ -706,6 +709,9 @@ static int ets_qdisc_init(struct Qdisc *sch, struct nlattr *opt,
 		return err;
 
 	INIT_LIST_HEAD(&q->active);
+	for (i = 0; i < TCQ_ETS_MAX_BANDS; i++)
+		INIT_LIST_HEAD(&q->classes[i].alist);
+
 	return ets_qdisc_change(sch, opt, extack);
 }
 

-- 
2.31.1

Hello:

This patch was applied to netdev/net-next.git (master)
by David S. Miller [off-list ref]:

On Thu,  7 Oct 2021 15:05:02 +0200 you wrote:

leaf classes of ETS qdiscs are served in strict priority or deficit round
robin (DRR), depending on the value of 'nstrict'. Since this value can be
changed while traffic is running, we need to be sure that the active list
of DRR classes can be updated at any time, so:

1) call INIT_LIST_HEAD(&alist) on all leaf classes in .init(), before the
   first packet hits any of them.
2) ensure that 'alist' is not overwritten with zeros when a leaf class is
   no more strict priority nor DRR (i.e. array elements beyond 'nbands').

[...]

Here is the summary with links:
  - [net-next] net/sched: sch_ets: properly init all active DRR list handles
    https://git.kernel.org/netdev/net-next/c/454d3e1ae057

You are awesome, thank you!
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