netdev - [PATCH net-next 3/3] net/sched: taprio: dynamic max_sdu larger than the max

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Date:   Thu, 16 Feb 2023 00:46:32 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Gerhard Engleder <gerhard@...leder-embedded.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH net-next 3/3] net/sched: taprio: dynamic max_sdu larger than the max_mtu is unlimited

It makes no sense to keep randomly large max_sdu values, especially if
larger than the device's max_mtu. These are visible in "tc qdisc show".
Such a max_sdu is practically unlimited and will cause no packets for
that traffic class to be dropped on enqueue.

Just set max_sdu_dynamic to U32_MAX, which in the logic below causes
taprio to save a max_frm_len of U32_MAX and a max_sdu presented to user
space of 0 (unlimited).

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/sched/sch_taprio.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 53ba4d6b0218..1f469861eae3 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -288,6 +288,8 @@ static void taprio_update_queue_max_sdu(struct taprio_sched *q,
 						    dev->hard_header_len + 1);
 			}
 			max_sdu_dynamic = max_frm_len - dev->hard_header_len;
+			if (max_sdu_dynamic > dev->max_mtu)
+				max_sdu_dynamic = U32_MAX;
 		}
 
 		max_sdu = min(max_sdu_dynamic, max_sdu_from_user);
-- 
2.34.1