tcp: make connect() mem charging friendly

[ Upstream commit 355a901e6cf1b2b763ec85caa2a9f04fbcc4ab4a ]

While working on sk_forward_alloc problems reported by Denys
Fedoryshchenko, we found that tcp connect() (and fastopen) do not call
sk_wmem_schedule() for SYN packet (and/or SYN/DATA packet), so
sk_forward_alloc is negative while connect is in progress.

We can fix this by calling regular sk_stream_alloc_skb() both for the
SYN packet (in tcp_connect()) and the syn_data packet in

Then, tcp_send_syn_data() can avoid copying syn_data as we simply
can manipulate syn_data->cb[] to remove SYN flag (and increment seq)

Instead of open coding memcpy_fromiovecend(), simply use this helper.

This leaves in socket write queue clean fast clone skbs.

This was tested against our fastopen packetdrill tests.

Reported-by: Denys Fedoryshchenko <>
Signed-off-by: Eric Dumazet <>
Acked-by: Yuchung Cheng <>
Signed-off-by: David S. Miller <>
[bwh: Backported to 3.2:
 - Drop the Fast Open changes
 - Adjust context]
Signed-off-by: Ben Hutchings <>
(cherry picked from commit 3e2eb8946907b2d53eb906e13e01d273c6534f5c)

Signed-off-by: Willy Tarreau <>
Signed-off-by: Stefan Bader <>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 0fc0a73..9e7fc38 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2378,13 +2378,10 @@
-	buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
-	if (unlikely(buff == NULL))
+	buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation);
+	if (unlikely(!buff))
 		return -ENOBUFS;
-	/* Reserve space for headers. */
-	skb_reserve(buff, MAX_TCP_HEADER);
 	tp->snd_nxt = tp->write_seq;
 	tcp_init_nondata_skb(buff, tp->write_seq++, TCPCB_FLAG_SYN);
 	TCP_ECN_send_syn(sk, buff);