[PATCH 4.14 36/40] tcp: inherit timestamp on mtu probe

From: Greg Kroah-Hartman
Date: Sun Sep 08 2019 - 08:59:12 EST

From: Willem de Bruijn <willemb@xxxxxxxxxx>

[ Upstream commit 888a5c53c0d8be6e98bc85b677f179f77a647873 ]

TCP associates tx timestamp requests with a byte in the bytestream.
If merging skbs in tcp_mtu_probe, migrate the tstamp request.

Similar to MSG_EOR, do not allow moving a timestamp from any segment
in the probe but the last. This to avoid merging multiple timestamps.

Tested with the packetdrill script at

Link: http://patchwork.ozlabs.org/patch/1143278/#2232897
Fixes: 4ed2d765dfac ("net-timestamp: TCP timestamping")
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/ipv4/tcp_output.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2025,7 +2025,7 @@ static bool tcp_can_coalesce_send_queue_
if (len <= skb->len)

- if (unlikely(TCP_SKB_CB(skb)->eor))
+ if (unlikely(TCP_SKB_CB(skb)->eor) || tcp_has_tx_tstamp(skb))
return false;

len -= skb->len;
@@ -2148,6 +2148,7 @@ static int tcp_mtu_probe(struct sock *sk
* we need to propagate it to the new skb.
TCP_SKB_CB(nskb)->eor = TCP_SKB_CB(skb)->eor;
+ tcp_skb_collapse_tstamp(nskb, skb);
tcp_unlink_write_queue(skb, sk);
sk_wmem_free_skb(sk, skb);
} else {