[PATCH net-next] tcp: fix TCP_REPAIR xmit queue setup

[PATCH net-next] tcp: fix TCP_REPAIR xmit queue setup

[Eric Dumazet]

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 5f6188a8003d ("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: 5f6188a8003d ("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>
---
 net/ipv4/tcp_output.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index d212e4cbc68902e873afb4a12b43b467ccd6069b..c07990a35ff3bd9438d32c82863ef207c93bdb9e 100644
--- a/net/ipv4/tcp_output.c
+++ b/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 (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);
+			/* "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);
+
 		cwnd_quota = tcp_cwnd_test(tp, skb);
 		if (!cwnd_quota) {
 			if (push_one == 2)
-- 
2.19.1.331.ge82ca0e54c-goog

Re: [PATCH net-next] tcp: fix TCP_REPAIR xmit queue setup

[David Miller]

From: Eric Dumazet <edumazet@google.com>
Date: Thu, 18 Oct 2018 09:12:19 -0700

> 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 5f6188a8003d ("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: 5f6188a8003d ("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>

Applied, thanks Eric.