net/sched: taprio: don't access q->qdiscs[] in unoffloaded mode during attach()

This is a simple code transformation with no intended behavior change,
just to make it absolutely clear that q->qdiscs[] is only attached to
the child taprio classes in full offload mode.

Right now we use the q->qdiscs[] variable in taprio_attach() for
software mode too, but that is quite confusing and avoidable. We use
it only to reach the netdev TX queue, but we could as well just use
netdev_get_tx_queue() for that.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20230807193324.4128292-2-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 8c9cfff7fd05c0f83cf2abdd18ecebdf72fb94d7..1cbc7fcd56c0a689bfce842a61b2127c747f07cf 100644 (file)
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -2145,14 +2145,20 @@ static void taprio_attach(struct Qdisc *sch)
 
        /* Attach underlying qdisc */
        for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
-               struct Qdisc *qdisc = q->qdiscs[ntx];
+               struct netdev_queue *dev_queue = netdev_get_tx_queue(dev, ntx);
                struct Qdisc *old;
 
                if (FULL_OFFLOAD_IS_ENABLED(q->flags)) {
+                       struct Qdisc *qdisc = q->qdiscs[ntx];
+
                        qdisc->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT;
-                       old = dev_graft_qdisc(qdisc->dev_queue, qdisc);
+                       old = dev_graft_qdisc(dev_queue, qdisc);
                } else {
-                       old = dev_graft_qdisc(qdisc->dev_queue, sch);
+                       /* In software mode, attach the root taprio qdisc
+                        * to all netdev TX queues, so that dev_qdisc_enqueue()
+                        * goes through taprio_enqueue().
+                        */
+                       old = dev_graft_qdisc(dev_queue, sch);
                        qdisc_refcount_inc(sch);
                }
                if (old)