Subject: [PATCH 19/49] tcp: Honor the eor bit in tcp_mtu_probe

From: Ilya Lesokhin <[email-masked]>
Date: Mon, 12 Feb 2018 12:57:04 +0200

[ Upstream commit 808cf9e38cd7923036a99f459ccc8cf2955e47af ]

Avoid SKB coalescing if eor bit is set in one of the relevant
SKBs.

Fixes: c134ecb87817 ("tcp: Make use of MSG_EOR in tcp_sendmsg")
Signed-off-by: Ilya Lesokhin <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/ipv4/tcp_output.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index cd3d60bb7cc8..7c1456bfa50e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1973,6 +1973,24 @@ static inline void tcp_mtu_check_reprobe(struct sock *sk)
 	}
 }
 
+static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len)
+{
+	struct sk_buff *skb, *next;
+
+	skb = tcp_send_head(sk);
+	tcp_for_write_queue_from_safe(skb, next, sk) {
+		if (len <= skb->len)
+			break;
+
+		if (unlikely(TCP_SKB_CB(skb)->eor))
+			return false;
+
+		len -= skb->len;
+	}
+
+	return true;
+}
+
 /* Create a new MTU probe if we are ready.
  * MTU probe is regularly attempting to increase the path MTU by
  * deliberately sending larger packets.  This discovers routing
@@ -2045,6 +2063,9 @@ static int tcp_mtu_probe(struct sock *sk)
 			return 0;
 	}
 
+	if (!tcp_can_coalesce_send_queue_head(sk, probe_size))
+		return -1;
+
 	/* We're allowed to probe.  Build it now. */
 	nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
 	if (!nskb)
@@ -2080,6 +2101,10 @@ static int tcp_mtu_probe(struct sock *sk)
 			/* We've eaten all the data from this skb.
 			 * Throw it away. */
 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
+			/* If this is the last SKB we copy and eor is set
+			 * we need to propagate it to the new skb.
+			 */
+			TCP_SKB_CB(nskb)->eor = TCP_SKB_CB(skb)->eor;
 			tcp_unlink_write_queue(skb, sk);
 			sk_wmem_free_skb(sk, skb);
 		} else {
-- 
2.14.3