tcp: provide skb->hash to synack packets

In commit b73c3d0e4f0e ("net: Save TX flow hash in sock and set in skbuf
on xmit"), Tom provided a l4 hash to most outgoing TCP packets.

We'd like to provide one as well for SYNACK packets, so that all packets
of a given flow share same txhash, to later enable bonding driver to
also use skb->hash to perform slave selection.

Note that a SYNACK retransmit shuffles the tx hash, as Tom did
in commit 265f94ff54d62 ("net: Recompute sk_txhash on negative routing
advice") for established sockets.

This has nice effect making TCP flows resilient to some kind of black
holes, even at connection establish phase.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Cc: Mahesh Bandewar <maheshb@google.com>
Acked-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 48c3696e86457172ff9e9a907db15e44b7e92bb5..937b97893d5f4877ecffc3f17de9bcb2fe3e3659 100644 (file)
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -113,6 +113,7 @@ struct tcp_request_sock {
        struct inet_request_sock        req;
        const struct tcp_request_sock_ops *af_specific;
        bool                            tfo_listener;
+       u32                             txhash;
        u32                             rcv_isn;
        u32                             snt_isn;
        u32                             snt_synack; /* synack sent time */

diff --git a/include/net/sock.h b/include/net/sock.h
index 7aa78440559a47db8e5ccc8ea69a34f87b90c125..94dff7f566f5cb2a7d2874f376f8d1a723ef7e13 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1654,12 +1654,16 @@ static inline void sock_graft(struct sock *sk, struct socket *parent)
 kuid_t sock_i_uid(struct sock *sk);
 unsigned long sock_i_ino(struct sock *sk);
 
-static inline void sk_set_txhash(struct sock *sk)
+static inline u32 net_tx_rndhash(void)
 {
-       sk->sk_txhash = prandom_u32();
+       u32 v = prandom_u32();
+
+       return v ?: 1;
+}
 
-       if (unlikely(!sk->sk_txhash))
-               sk->sk_txhash = 1;
+static inline void sk_set_txhash(struct sock *sk)
+{
+       sk->sk_txhash = net_tx_rndhash();
 }
 
 static inline void sk_rethink_txhash(struct sock *sk)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a8f515bb19c4bbd2d379c6f5c29f9a3d02e8bc96..a62e9c76d485fb1f316da1323a9982d3d3019e94 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6228,6 +6228,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
        }
 
        tcp_rsk(req)->snt_isn = isn;
+       tcp_rsk(req)->txhash = net_tx_rndhash();
        tcp_openreq_init_rwin(req, sk, dst);
        fastopen = !want_cookie &&
                   tcp_try_fastopen(sk, skb, req, &foc, dst);

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 93898e093d4e655537665602337de3c6c35cab70..d671d742a2398d04ce2d6f5126ab941a36bbc1cc 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1276,8 +1276,8 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
        newinet->mc_index     = inet_iif(skb);
        newinet->mc_ttl       = ip_hdr(skb)->ttl;
        newinet->rcv_tos      = ip_hdr(skb)->tos;
+       newsk->sk_txhash      = tcp_rsk(req)->txhash;
        inet_csk(newsk)->icsk_ext_hdr_len = 0;
-       sk_set_txhash(newsk);
        if (inet_opt)
                inet_csk(newsk)->icsk_ext_hdr_len = inet_opt->opt.optlen;
        newinet->inet_id = newtp->write_seq ^ jiffies;

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f9a8a12b62ee64d954ae9a4aab75bcdce687650b..d0ad3554c3332b5f32c48e7dcf28cf05484754a8 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2987,6 +2987,7 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
        rcu_read_lock();
        md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
 #endif
+       skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
        tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, md5,
                                             foc) + sizeof(*th);
 
@@ -3505,6 +3506,7 @@ int tcp_rtx_synack(struct sock *sk, struct request_sock *req)
        struct flowi fl;
        int res;
 
+       tcp_rsk(req)->txhash = net_tx_rndhash();
        res = af_ops->send_synack(sk, NULL, &fl, req, 0, NULL);
        if (!res) {
                TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 97d9314ea3611eeadd576d2fd8919ae60d468891..f9c0e264067104260ed586836364da10019851aa 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1090,7 +1090,7 @@ static struct sock *tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
        newsk->sk_v6_rcv_saddr = ireq->ir_v6_loc_addr;
        newsk->sk_bound_dev_if = ireq->ir_iif;
 
-       sk_set_txhash(newsk);
+       newsk->sk_txhash = tcp_rsk(req)->txhash;
 
        /* Now IPv6 options...