net/sched: sch_htb: do not change sch->flags in htb_dump()

[ Upstream commit 9b949fa ]

htb_dump() runs without holding qdisc spinlock.

It is illegal to touch sch->flags with non locked RMW,
as concurrent readers might see intermediate wrong values.

Set TCQ_F_OFFLOADED in control path (htb_init()) instead.

Fixes: d03b195 ("sch_htb: Hierarchical QoS hardware offload")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260514095935.3926276-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: edumazet

net/sched/sch_htb.c

@@ -1148,6 +1148,7 @@ static int htb_init(struct Qdisc *sch, struct nlattr *opt,
 	 * parts (especially calling ndo_setup_tc) on errors.
 	 */
 	q->offload = true;
+	sch->flags |= TCQ_F_OFFLOADED;
 
 	return 0;
 }
@@ -1208,11 +1209,6 @@ static int htb_dump(struct Qdisc *sch, struct sk_buff *skb)
 	struct nlattr *nest;
 	struct tc_htb_glob gopt;
 
-	if (q->offload)
-		sch->flags |= TCQ_F_OFFLOADED;
-	else
-		sch->flags &= ~TCQ_F_OFFLOADED;
-
 	sch->qstats.overlimits = q->overlimits;
 	/* Its safe to not acquire qdisc lock. As we hold RTNL,
 	 * no change can happen on the qdisc parameters.