tcp: move duplicate code from tcp_v4_init_sock()/tcp_v6_init_sock()

This commit moves the (substantial) common code shared between
tcp_v4_init_sock() and tcp_v6_init_sock() to a new address-family
independent function, tcp_init_sock().

Centralizing this functionality should help avoid drift issues,
e.g. where the IPv4 side is updated without a corresponding update to
IPv6. There was already some drift: IPv4 initialized snd_cwnd to
TCP_INIT_CWND, while the IPv6 side was still initializing snd_cwnd to
2 (in this case it should not matter, since snd_cwnd is also
initialized in tcp_init_metrics(), but the general risks and
maintenance overhead remain).

When diffing the old and new code, note that new tcp_init_sock()
function uses the order of steps from the tcp_v4_init_sock()
implementation (the order is slightly different in
tcp_v6_init_sock()).

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 66 insertions, 50 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3ce3bd031f3..bcc4eab5f25 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -363,6 +363,70 @@ static int retrans_to_secs(u8 retrans, int timeout, int rto_max)
         return period;
 }
 
+/* Address-family independent initialization for a tcp_sock.
+ *
+ * NOTE: A lot of things set to zero explicitly by call to
+ *       sk_alloc() so need not be done here.
+ */
+void tcp_init_sock(struct sock *sk)
+{
+        struct inet_connection_sock *icsk = inet_csk(sk);
+        struct tcp_sock *tp = tcp_sk(sk);
+
+        skb_queue_head_init(&tp->out_of_order_queue);
+        tcp_init_xmit_timers(sk);
+        tcp_prequeue_init(tp);
+
+        icsk->icsk_rto = TCP_TIMEOUT_INIT;
+        tp->mdev = TCP_TIMEOUT_INIT;
+
+        /* So many TCP implementations out there (incorrectly) count the
+         * initial SYN frame in their delayed-ACK and congestion control
+         * algorithms that we must have the following bandaid to talk
+         * efficiently to them.  -DaveM
+         */
+        tp->snd_cwnd = TCP_INIT_CWND;
+
+        /* See draft-stevens-tcpca-spec-01 for discussion of the
+         * initialization of these values.
+         */
+        tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
+        tp->snd_cwnd_clamp = ~0;
+        tp->mss_cache = TCP_MSS_DEFAULT;
+
+        tp->reordering = sysctl_tcp_reordering;
+        icsk->icsk_ca_ops = &tcp_init_congestion_ops;
+
+        sk->sk_state = TCP_CLOSE;
+
+        sk->sk_write_space = sk_stream_write_space;
+        sock_set_flag(sk, SOCK_USE_WRITE_QUEUE);
+
+        icsk->icsk_sync_mss = tcp_sync_mss;
+
+        /* TCP Cookie Transactions */
+        if (sysctl_tcp_cookie_size > 0) {
+                /* Default, cookies without s_data_payload. */
+                tp->cookie_values =
+                        kzalloc(sizeof(*tp->cookie_values),
+                                sk->sk_allocation);
+                if (tp->cookie_values != NULL)
+                        kref_init(&tp->cookie_values->kref);
+        }
+        /* Presumed zeroed, in order of appearance:
+         *      cookie_in_always, cookie_out_never,
+         *      s_data_constant, s_data_in, s_data_out
+         */
+        sk->sk_sndbuf = sysctl_tcp_wmem[1];
+        sk->sk_rcvbuf = sysctl_tcp_rmem[1];
+
+        local_bh_disable();
+        sock_update_memcg(sk);
+        sk_sockets_allocated_inc(sk);
+        local_bh_enable();
+}
+EXPORT_SYMBOL(tcp_init_sock);
+
 /*
  *      Wait for a TCP event.
  *
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index ba6dad81908..5b07ea10930 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1890,62 +1890,14 @@ static int tcp_v4_init_sock(struct sock *sk)
         struct inet_connection_sock *icsk = inet_csk(sk);
         struct tcp_sock *tp = tcp_sk(sk);
 
-        skb_queue_head_init(&tp->out_of_order_queue);
-        tcp_init_xmit_timers(sk);
-        tcp_prequeue_init(tp);
-
-        icsk->icsk_rto = TCP_TIMEOUT_INIT;
-        tp->mdev = TCP_TIMEOUT_INIT;
-
-        /* So many TCP implementations out there (incorrectly) count the
-         * initial SYN frame in their delayed-ACK and congestion control
-         * algorithms that we must have the following bandaid to talk
-         * efficiently to them.  -DaveM
-         */
-        tp->snd_cwnd = TCP_INIT_CWND;
-
-        /* See draft-stevens-tcpca-spec-01 for discussion of the
-         * initialization of these values.
-         */
-        tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
-        tp->snd_cwnd_clamp = ~0;
-        tp->mss_cache = TCP_MSS_DEFAULT;
-
-        tp->reordering = sysctl_tcp_reordering;
-        icsk->icsk_ca_ops = &tcp_init_congestion_ops;
-
-        sk->sk_state = TCP_CLOSE;
-
-        sk->sk_write_space = sk_stream_write_space;
-        sock_set_flag(sk, SOCK_USE_WRITE_QUEUE);
+        tcp_init_sock(sk);
 
         icsk->icsk_af_ops = &ipv4_specific;
-        icsk->icsk_sync_mss = tcp_sync_mss;
+
 #ifdef CONFIG_TCP_MD5SIG
         tp->af_specific = &tcp_sock_ipv4_specific;
 #endif
 
-        /* TCP Cookie Transactions */
-        if (sysctl_tcp_cookie_size > 0) {
-                /* Default, cookies without s_data_payload. */
-                tp->cookie_values =
-                        kzalloc(sizeof(*tp->cookie_values),
-                                sk->sk_allocation);
-                if (tp->cookie_values != NULL)
-                        kref_init(&tp->cookie_values->kref);
-        }
-        /* Presumed zeroed, in order of appearance:
-         *      cookie_in_always, cookie_out_never,
-         *      s_data_constant, s_data_in, s_data_out
-         */
-        sk->sk_sndbuf = sysctl_tcp_wmem[1];
-        sk->sk_rcvbuf = sysctl_tcp_rmem[1];
-
-        local_bh_disable();
-        sock_update_memcg(sk);
-        sk_sockets_allocated_inc(sk);
-        local_bh_enable();
-
         return 0;
 }