net_sched: sch_fq: fastpath needs to take care of sk->sk_pacing_status

If packets of a TCP flows take the fast path, we need to make sure
sk->sk_pacing_status is set to SK_PACING_FQ otherwise TCP might
fallback to internal pacing, which is not optimal.

Fixes: 076433bd ("net_sched: sch_fq: add fast path for mostly idle qdisc")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20231020201254.732527-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/sch_fq.c

@@ -383,6 +383,10 @@ static struct fq_flow *fq_classify(struct Qdisc *sch, struct sk_buff *skb,
 
 	if (fq_fastpath_check(sch, skb, now)) {
 		q->internal.stat_fastpath_packets++;
+		if (skb->sk == sk && q->rate_enable &&
+		    READ_ONCE(sk->sk_pacing_status) != SK_PACING_FQ)
+			smp_store_release(&sk->sk_pacing_status,
+					  SK_PACING_FQ);
 		return &q->internal;
 	}