[PATCH net] net/smc: fix fallback failed while sendmsg with fastopen

["D. Wythe" <alibuda@linux.alibaba.com>]

From: "D. Wythe" <alibuda@linux.alibaba.com>

Before determining whether the msg has unsupported options, it has been
prematurely terminated by the wrong status check.

For the application, the general method of MSG_FASTOPEN likes

fd = socket(...)
/* rather than connect */
sendto(fd, data, len, MSG_FASTOPEN)

Hence, We need to check the flag before state check, because the sock state
here is always SMC_INIT when applications tries MSG_FASTOPEN. Once we
found unsupported options, fallback it to TCP.

Fixes: ee9dfbef02d1 ("net/smc: handle sockopts forcing fallback")
Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
 net/smc/af_smc.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index b233c94..fd80879 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -2662,24 +2662,30 @@ static int smc_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 	int rc = -EPIPE;
 
 	smc = smc_sk(sk);
-	lock_sock(sk);
-	if ((sk->sk_state != SMC_ACTIVE) &&
-	    (sk->sk_state != SMC_APPCLOSEWAIT1) &&
-	    (sk->sk_state != SMC_INIT))
-		goto out;
 
+	/* SMC do not support connect with fastopen */
 	if (msg->msg_flags & MSG_FASTOPEN) {
+		rc = -EINVAL;
+		lock_sock(sk);
+		/* not perform connect yet, fallback it */
 		if (sk->sk_state == SMC_INIT && !smc->connect_nonblock) {
 			rc = smc_switch_to_fallback(smc, SMC_CLC_DECL_OPTUNSUPP);
-			if (rc)
-				goto out;
-		} else {
-			rc = -EINVAL;
-			goto out;
+			/*  fallback success */
+			if (rc == 0)
+				goto fallback;	/* with sock lock hold */
 		}
+		release_sock(sk);
+		return rc;
 	}
 
+	lock_sock(sk);
+	if (sk->sk_state != SMC_ACTIVE &&
+	    sk->sk_state != SMC_APPCLOSEWAIT1 &&
+	    sk->sk_state != SMC_INIT)
+		goto out;
+
 	if (smc->use_fallback) {
+fallback:
 		rc = smc->clcsock->ops->sendmsg(smc->clcsock, msg, len);
 	} else {
 		rc = smc_tx_sendmsg(smc, msg, len);
-- 
1.8.3.1