[RFC PATCH v3 net-next 2/3] tcp: Handle eor bit when coalescing skb

[Martin KaFai Lau <kafai@fb.com>]

This patch:
1. Prevent next_skb from coalescing to the prev_skb if
   TCP_SKB_CB(prev_skb)->eor is set
2. Update the TCP_SKB_CB(prev_skb)->eor if coalescing is
   allowed

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
---
 net/ipv4/tcp_input.c  | 4 ++++
 net/ipv4/tcp_output.c | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 75e8336..68c55e5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1303,6 +1303,7 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 	}
 
 	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
+	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
 		TCP_SKB_CB(prev)->end_seq++;
 
@@ -1368,6 +1369,9 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
 	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
 		goto fallback;
 
+	if (TCP_SKB_CB(prev)->eor)
+		goto fallback;
+
 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a6e4a83..96bdf98 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2494,6 +2494,7 @@ static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
 	 * packet counting does not break.
 	 */
 	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
+	TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
 
 	/* changed transmit queue under us so clear hints */
 	tcp_clear_retrans_hints_partial(tp);
@@ -2545,6 +2546,9 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
 		if (!tcp_can_collapse(sk, skb))
 			break;
 
+		if (TCP_SKB_CB(to)->eor)
+			break;
+
 		space -= skb->len;
 
 		if (first) {
-- 
2.5.1