tcp: fix TCP_REPAIR xmit queue setup

Andrey reported the following warning triggered while running CRIU tests:

tcp_clean_rtx_queue()
...
	last_ackt = tcp_skb_timestamp_us(skb);
	WARN_ON_ONCE(last_ackt == 0);

This is caused by 5f6188a800 ("tcp: do not change tcp_wstamp_ns
in tcp_mstamp_refresh"), as we end up having skbs in retransmit queue
with a zero skb->skb_mstamp_ns field.

We could fix this bug in different ways, like making sure
tp->tcp_wstamp_ns is not zero at socket creation, but as Neal pointed
out, we also do not want that pacing status of a repaired socket
could push tp->tcp_wstamp_ns far ahead in the future.

So we prefer changing tcp_write_xmit() to not call tcp_update_skb_after_send()
and instead do what is requested by TCP_REPAIR logic.

Fixes: 5f6188a800 ("tcp: do not change tcp_wstamp_ns in tcp_mstamp_refresh")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

@@ -2321,18 +2321,19 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 	while ((skb = tcp_send_head(sk))) {
 		unsigned int limit;
 
+		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
+			/* "skb_mstamp_ns" is used as a start point for the retransmit timer */
+			skb->skb_mstamp_ns = tp->tcp_wstamp_ns = tp->tcp_clock_cache;
+			list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue);
+			goto repair; /* Skip network transmission */
+		}
+
 		if (tcp_pacing_check(sk))
 			break;
 
 		tso_segs = tcp_init_tso_segs(skb, mss_now);
 		BUG_ON(!tso_segs);
 
-		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
-			/* "skb_mstamp" is used as a start point for the retransmit timer */
-			tcp_update_skb_after_send(sk, skb, tp->tcp_wstamp_ns);
-			goto repair; /* Skip network transmission */
-		}
-
 		cwnd_quota = tcp_cwnd_test(tp, skb);
 		if (!cwnd_quota) {
 			if (push_one == 2)