net/smc: propagate file from SMC to TCP socket

fcntl(fd, F_SETOWN, getpid()) selects the recipient of SIGURG signals
that are delivered when out-of-band data arrives on socket fd.
If an SMC socket program makes use of such an fcntl() call, it fails
in case of fallback to TCP-mode. In case of fallback the traffic is
processed with the internal TCP socket. Propagating field "file" from the
SMC socket to the internal TCP socket fixes the issue.

Reviewed-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -2084,12 +2084,6 @@ static inline bool skwq_has_sleeper(struct socket_wq *wq)
  * @p:              poll_table
  *
  * See the comments in the wq_has_sleeper function.
- *
- * Do not derive sock from filp->private_data here. An SMC socket establishes
- * an internal TCP socket that is used in the fallback case. All socket
- * operations on the SMC socket are then forwarded to the TCP socket. In case of
- * poll, the filp->private_data pointer references the SMC socket because the
- * TCP socket has no file assigned.
  */
 static inline void sock_poll_wait(struct file *filp, struct socket *sock,
 				  poll_table *p)

net/smc/af_smc.c

@@ -445,10 +445,19 @@ static void smc_link_save_peer_info(struct smc_link *link,
 	link->peer_mtu = clc->qp_mtu;
 }
 
+static void smc_switch_to_fallback(struct smc_sock *smc)
+{
+	smc->use_fallback = true;
+	if (smc->sk.sk_socket && smc->sk.sk_socket->file) {
+		smc->clcsock->file = smc->sk.sk_socket->file;
+		smc->clcsock->file->private_data = smc->clcsock;
+	}
+}
+
 /* fall back during connect */
 static int smc_connect_fallback(struct smc_sock *smc, int reason_code)
 {
-	smc->use_fallback = true;
+	smc_switch_to_fallback(smc);
 	smc->fallback_rsn = reason_code;
 	smc_copy_sock_settings_to_clc(smc);
 	if (smc->sk.sk_state == SMC_INIT)
@@ -774,10 +783,14 @@ static void smc_connect_work(struct work_struct *work)
 		smc->sk.sk_err = -rc;
 
 out:
-	if (smc->sk.sk_err)
-		smc->sk.sk_state_change(&smc->sk);
-	else
-		smc->sk.sk_write_space(&smc->sk);
+	if (!sock_flag(&smc->sk, SOCK_DEAD)) {
+		if (smc->sk.sk_err) {
+			smc->sk.sk_state_change(&smc->sk);
+		} else { /* allow polling before and after fallback decision */
+			smc->clcsock->sk->sk_write_space(smc->clcsock->sk);
+			smc->sk.sk_write_space(&smc->sk);
+		}
+	}
 	kfree(smc->connect_info);
 	smc->connect_info = NULL;
 	release_sock(&smc->sk);
@@ -934,8 +947,13 @@ struct sock *smc_accept_dequeue(struct sock *parent,
 			sock_put(new_sk); /* final */
 			continue;
 		}
-		if (new_sock)
+		if (new_sock) {
 			sock_graft(new_sk, new_sock);
+			if (isk->use_fallback) {
+				smc_sk(new_sk)->clcsock->file = new_sock->file;
+				isk->clcsock->file->private_data = isk->clcsock;
+			}
+		}
 		return new_sk;
 	}
 	return NULL;
@@ -1086,7 +1104,7 @@ static void smc_listen_decline(struct smc_sock *new_smc, int reason_code,
 		return;
 	}
 	smc_conn_free(&new_smc->conn);
-	new_smc->use_fallback = true;
+	smc_switch_to_fallback(new_smc);
 	new_smc->fallback_rsn = reason_code;
 	if (reason_code && reason_code != SMC_CLC_DECL_PEERDECL) {
 		if (smc_clc_send_decline(new_smc, reason_code) < 0) {
@@ -1246,7 +1264,7 @@ static void smc_listen_work(struct work_struct *work)
 
 	/* check if peer is smc capable */
 	if (!tcp_sk(newclcsock->sk)->syn_smc) {
-		new_smc->use_fallback = true;
+		smc_switch_to_fallback(new_smc);
 		new_smc->fallback_rsn = SMC_CLC_DECL_PEERNOSMC;
 		smc_listen_out_connected(new_smc);
 		return;
@@ -1503,7 +1521,7 @@ static int smc_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 
 	if (msg->msg_flags & MSG_FASTOPEN) {
 		if (sk->sk_state == SMC_INIT) {
-			smc->use_fallback = true;
+			smc_switch_to_fallback(smc);
 			smc->fallback_rsn = SMC_CLC_DECL_OPTUNSUPP;
 		} else {
 			rc = -EINVAL;
@@ -1705,7 +1723,7 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
 	case TCP_FASTOPEN_NO_COOKIE:
 		/* option not supported by SMC */
 		if (sk->sk_state == SMC_INIT) {
-			smc->use_fallback = true;
+			smc_switch_to_fallback(smc);
 			smc->fallback_rsn = SMC_CLC_DECL_OPTUNSUPP;
 		} else {
 			if (!smc->use_fallback)