rds: RDS (tcp) hangs on sendto() to unresponding address

In rds_send_mprds_hash(), if the calculated hash value is non-zero and
the MPRDS connections are not yet up, it will wait.  But it should not
wait if the send is non-blocking.  In this case, it should just use the
base c_path for sending the message.

Orabug: 28720880

Signed-off-by: Ka-Cheong Poon <[email protected]>
Reviewed-by: Sowmini Varadhan <[email protected]>
Reviewed-by: Santosh Shilimkar <[email protected]>

Author: kcp-git

net/rds/send.c

@@ -1182,7 +1182,8 @@ static inline int rds_rdma_bytes(struct msghdr *msg, size_t *rdma_bytes)
 	return 0;
 }
 
-static int rds_send_mprds_hash(struct rds_sock *rs, struct rds_connection *conn)
+static int rds_send_mprds_hash(struct rds_sock *rs,
+			       struct rds_connection *conn, int nonblock)
 {
 	int hash;
 
@@ -1198,10 +1199,16 @@ static int rds_send_mprds_hash(struct rds_sock *rs, struct rds_connection *conn)
 		 * used.  But if we are interrupted, we have to use the zero
 		 * c_path in case the connection ends up being non-MP capable.
 		 */
-		if (conn->c_npaths == 0)
+		if (conn->c_npaths == 0) {
+			/* Cannot wait for the connection be made, so just use
+			 * the base c_path.
+			 */
+			if (nonblock)
+				return 0;
 			if (wait_event_interruptible(conn->c_hs_waitq,
 						     conn->c_npaths != 0))
 				hash = 0;
+		}
 		if (conn->c_npaths == 1)
 			hash = 0;
 	}
@@ -1433,7 +1440,7 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
 	}
 
 	if (conn->c_trans->t_mp_capable)
-		cpath = &conn->c_path[rds_send_mprds_hash(rs, conn)];
+		cpath = &conn->c_path[rds_send_mprds_hash(rs, conn, nonblock)];
 	else
 		cpath = &conn->c_path[0];