netdev - [PATCH v2 net-next 3/9] net/sched: taprio: try again to report q->qdiscs[] to qdisc

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Date: Wed, 14 Jun 2023 00:54:34 +0300
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>,
	linux-kernel@...r.kernel.org,
	intel-wired-lan@...ts.osuosl.org,
	Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@...el.com>,
	Peilin Ye <yepeilin.cs@...il.com>,
	Pedro Tammela <pctammela@...atatu.com>,
	Richard Cochran <richardcochran@...il.com>,
	Zhengchao Shao <shaozhengchao@...wei.com>,
	Maxim Georgiev <glipus@...il.com>
Subject: [PATCH v2 net-next 3/9] net/sched: taprio: try again to report q->qdiscs[] to qdisc_leaf()

This is another stab at commit 1461d212ab27 ("net/sched: taprio: make
qdisc_leaf() see the per-netdev-queue pfifo child qdiscs"), later
reverted in commit af7b29b1deaa ("Revert "net/sched: taprio: make
qdisc_leaf() see the per-netdev-queue pfifo child qdiscs"").

I believe that the problems that caused the revert were fixed, and thus,
this change is identical to the original patch.

Its purpose is to properly reject attaching a software taprio child
qdisc to a software taprio parent. Because unoffloaded taprio currently
reports itself (the root Qdisc) as the return value from qdisc_leaf(),
then the process of attaching another taprio as child to a Qdisc class
of the root will just result in a Qdisc_ops :: change() call for the
root. Whereas that's not we want. We want Qdisc_ops :: init() to be
called for the taprio child, in order to give the taprio child a chance
to check whether its sch->parent is TC_H_ROOT or not (and reject this
configuration).

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
v1->v2: rebase on top of rtnl_dereference() change for txq->qdisc_sleeping

 net/sched/sch_taprio.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index b5f533914415..14d628926d61 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -2439,12 +2439,14 @@ static int taprio_dump(struct Qdisc *sch, struct sk_buff *skb)

 static struct Qdisc *taprio_leaf(struct Qdisc *sch, unsigned long cl)
 {
-	struct netdev_queue *dev_queue = taprio_queue_get(sch, cl);
+	struct taprio_sched *q = qdisc_priv(sch);
+	struct net_device *dev = qdisc_dev(sch);
+	unsigned int ntx = cl - 1;

-	if (!dev_queue)
+	if (ntx >= dev->num_tx_queues)
 		return NULL;

-	return rtnl_dereference(dev_queue->qdisc_sleeping);
+	return q->qdiscs[ntx];
 }

 static unsigned long taprio_find(struct Qdisc *sch, u32 classid)
-- 
2.34.1