inet: factor out locked section of inet_accept() in a new helper

No functional changes intended. The new helper will be used
by the MPTCP protocol in the next patch to avoid duplicating
a few LoC.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/inet_common.h

@@ -31,6 +31,8 @@ int inet_dgram_connect(struct socket *sock, struct sockaddr *uaddr,
 		       int addr_len, int flags);
 int inet_accept(struct socket *sock, struct socket *newsock, int flags,
 		bool kern);
+void __inet_accept(struct socket *sock, struct socket *newsock,
+		   struct sock *newsk);
 int inet_send_prepare(struct sock *sk);
 int inet_sendmsg(struct socket *sock, struct msghdr *msg, size_t size);
 ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset,

net/ipv4/af_inet.c

@@ -730,6 +730,20 @@ int inet_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 }
 EXPORT_SYMBOL(inet_stream_connect);
 
+void __inet_accept(struct socket *sock, struct socket *newsock, struct sock *newsk)
+{
+	sock_rps_record_flow(newsk);
+	WARN_ON(!((1 << newsk->sk_state) &
+		  (TCPF_ESTABLISHED | TCPF_SYN_RECV |
+		  TCPF_CLOSE_WAIT | TCPF_CLOSE)));
+
+	if (test_bit(SOCK_SUPPORT_ZC, &sock->flags))
+		set_bit(SOCK_SUPPORT_ZC, &newsock->flags);
+	sock_graft(newsk, newsock);
+
+	newsock->state = SS_CONNECTED;
+}
+
 /*
  *	Accept a pending connection. The TCP layer now gives BSD semantics.
  */
@@ -743,24 +757,12 @@ int inet_accept(struct socket *sock, struct socket *newsock, int flags,
 	/* IPV6_ADDRFORM can change sk->sk_prot under us. */
 	sk2 = READ_ONCE(sk1->sk_prot)->accept(sk1, flags, &err, kern);
 	if (!sk2)
-		goto do_err;
+		return err;
 
 	lock_sock(sk2);
-
-	sock_rps_record_flow(sk2);
-	WARN_ON(!((1 << sk2->sk_state) &
-		  (TCPF_ESTABLISHED | TCPF_SYN_RECV |
-		  TCPF_CLOSE_WAIT | TCPF_CLOSE)));
-
-	if (test_bit(SOCK_SUPPORT_ZC, &sock->flags))
-		set_bit(SOCK_SUPPORT_ZC, &newsock->flags);
-	sock_graft(sk2, newsock);
-
-	newsock->state = SS_CONNECTED;
-	err = 0;
+	__inet_accept(sock, newsock, sk2);
 	release_sock(sk2);
-do_err:
-	return err;
+	return 0;
 }
 EXPORT_SYMBOL(inet_accept);