net_sched: sch_fq: properly set sk->sk_pacing_status

If fq_classify() recycles a struct fq_flow because
a socket structure has been reallocated, we do not
set sk->sk_pacing_status immediately, but later if the
flow becomes detached.

This means that any flow requiring pacing (BBR, or SO_MAX_PACING_RATE)
might fallback to TCP internal pacing, which requires a per-socket
high resolution timer, and therefore more cpu cycles.

Fixes: 218af599 ("tcp: internal implementation for pacing")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_fq.c

@@ -301,6 +301,9 @@ static struct fq_flow *fq_classify(struct sk_buff *skb, struct fq_sched_data *q)
 				     f->socket_hash != sk->sk_hash)) {
 				f->credit = q->initial_quantum;
 				f->socket_hash = sk->sk_hash;
+				if (q->rate_enable)
+					smp_store_release(&sk->sk_pacing_status,
+							  SK_PACING_FQ);
 				if (fq_flow_is_throttled(f))
 					fq_flow_unset_throttled(q, f);
 				f->time_next_packet = 0ULL;
@@ -322,8 +325,12 @@ static struct fq_flow *fq_classify(struct sk_buff *skb, struct fq_sched_data *q)
 
 	fq_flow_set_detached(f);
 	f->sk = sk;
-	if (skb->sk == sk)
+	if (skb->sk == sk) {
 		f->socket_hash = sk->sk_hash;
+		if (q->rate_enable)
+			smp_store_release(&sk->sk_pacing_status,
+					  SK_PACING_FQ);
+	}
 	f->credit = q->initial_quantum;
 
 	rb_link_node(&f->fq_node, parent, p);
@@ -428,17 +435,9 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	f->qlen++;
 	qdisc_qstats_backlog_inc(sch, skb);
 	if (fq_flow_is_detached(f)) {
-		struct sock *sk = skb->sk;
-
 		fq_flow_add_tail(&q->new_flows, f);
 		if (time_after(jiffies, f->age + q->flow_refill_delay))
 			f->credit = max_t(u32, f->credit, q->quantum);
-		if (sk && q->rate_enable) {
-			if (unlikely(smp_load_acquire(&sk->sk_pacing_status) !=
-				     SK_PACING_FQ))
-				smp_store_release(&sk->sk_pacing_status,
-						  SK_PACING_FQ);
-		}
 		q->inactive_flows--;
 	}