tcp: inherit timestamp on mtu probe

[ 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
https://github.com/wdebruij/packetdrill/commits/mtu_probe-1

Link: http://patchwork.ozlabs.org/patch/1143278/#2232897
Fixes: 4ed2d765dfac ("net-timestamp: TCP timestamping")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a99086bf26eaf2d83c6f7a0c497f36787f150308..5b808089eff89c44f3afda51652f2fe9e3416fed 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2025,7 +2025,7 @@ static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len)
                if (len <= skb->len)
                        break;
 
-               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 {