[PATCH v5 1/1] tcp: Honor the eor bit in tcp_mtu_probe

[Ilya Lesokhin <ilyal@mellanox.com>]

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 <ilyal@mellanox.com>
---
Changes from v4:
- Remove Gerrit Change-Id

Changes from v3:
- Fix coding style

Changes from v2:                                                                 
- Initialize SKB before tcp_for_write_queue_from_safe                            
- Move new logic to its own function
- Add comment about eor propagation
                                                                                 
Changes from v1:                                                                 
- Propagate eor when consuming the old SKB 

 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 e9f985e42405..b2bca373f8be 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2027,6 +2027,24 @@ 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
@@ -2099,6 +2117,9 @@ 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)
@@ -2134,6 +2155,10 @@ 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 {
-- 
2.15.0.317.g14c63a9