netdev - [PATCH net] sch_htb: Avoid grafting on htb_destroy_class

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Date:   Tue, 10 Jan 2023 12:20:04 -0800
From:   Rahul Rameshbabu <rrameshbabu@...dia.com>
To:     netdev@...r.kernel.org
Cc:     Tariq Toukan <tariqt@...dia.com>, Gal Pressman <gal@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Miller <davem@...emloft.net>,
        Rahul Rameshbabu <rrameshbabu@...dia.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Maxim Mikityanskiy <maxtram95@...il.com>
Subject: [PATCH net] sch_htb: Avoid grafting on htb_destroy_class_offload when destroying htb

Peek at old qdisc and graft only when deleting leaf class in the htb. When
destroying the htb, the caller may already have grafted a new qdisc that is
not part of the htb structure being destroyed. htb_destroy_class_offload
should not peek at the qdisc of the netdev queue since that will either be
the new qdisc in the case of replacing the htb or simply a noop_qdisc is
the case of destroying the htb without a replacement qdisc.

Fixes: d03b195b5aa0 ("sch_htb: Hierarchical QoS hardware offload")
Signed-off-by: Rahul Rameshbabu <rrameshbabu@...dia.com>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Maxim Mikityanskiy <maxtram95@...il.com>
---
 net/sched/sch_htb.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 2238edece1a4..360ce8616fd2 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1557,14 +1557,13 @@ static int htb_destroy_class_offload(struct Qdisc *sch, struct htb_class *cl,
 
 	WARN_ON(!q);
 	dev_queue = htb_offload_get_queue(cl);
-	old = htb_graft_helper(dev_queue, NULL);
-	if (destroying)
-		/* Before HTB is destroyed, the kernel grafts noop_qdisc to
-		 * all queues.
+	if (!destroying) {
+		old = htb_graft_helper(dev_queue, NULL);
+		/* Last qdisc grafted should be the same as cl->leaf.q when
+		 * calling htb_destroy
 		 */
-		WARN_ON(!(old->flags & TCQ_F_BUILTIN));
-	else
 		WARN_ON(old != q);
+	}
 
 	if (cl->parent) {
 		_bstats_update(&cl->parent->bstats_bias,
@@ -1581,10 +1580,14 @@ static int htb_destroy_class_offload(struct Qdisc *sch, struct htb_class *cl,
 	};
 	err = htb_offload(qdisc_dev(sch), &offload_opt);
 
-	if (!err || destroying)
-		qdisc_put(old);
-	else
-		htb_graft_helper(dev_queue, old);
+	/* htb_offload related errors when destroying cannot be handled */
+	WARN_ON(err && destroying);
+	if (!destroying) {
+		if (!err)
+			qdisc_put(old);
+		else
+			htb_graft_helper(dev_queue, old);
+	}
 
 	if (last_child)
 		return err;
-- 
2.36.2