SUNRPC: Fix an Oops in udp_poll()

udp_poll() checks the struct file for the O_NONBLOCK flag, so we must not
call it with a NULL file pointer.

Fixes: 0ffe86f4 ("SUNRPC: Use poll() to fix up the socket requeue races")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

include/linux/sunrpc/xprtsock.h

@@ -26,6 +26,7 @@ struct sock_xprt {
 	 */
 	struct socket *		sock;
 	struct sock *		inet;
+	struct file *		file;
 
 	/*
 	 * State of TCP reply receive

net/sunrpc/xprtsock.c

@@ -670,7 +670,8 @@ xs_read_stream(struct sock_xprt *transport, int flags)
 
 static __poll_t xs_poll_socket(struct sock_xprt *transport)
 {
-	return transport->sock->ops->poll(NULL, transport->sock, NULL);
+	return transport->sock->ops->poll(transport->file, transport->sock,
+			NULL);
 }
 
 static bool xs_poll_socket_readable(struct sock_xprt *transport)
@@ -1253,6 +1254,7 @@ static void xs_reset_transport(struct sock_xprt *transport)
 	struct socket *sock = transport->sock;
 	struct sock *sk = transport->inet;
 	struct rpc_xprt *xprt = &transport->xprt;
+	struct file *filp = transport->file;
 
 	if (sk == NULL)
 		return;
@@ -1266,6 +1268,7 @@ static void xs_reset_transport(struct sock_xprt *transport)
 	write_lock_bh(&sk->sk_callback_lock);
 	transport->inet = NULL;
 	transport->sock = NULL;
+	transport->file = NULL;
 
 	sk->sk_user_data = NULL;
 
@@ -1278,7 +1281,7 @@ static void xs_reset_transport(struct sock_xprt *transport)
 	mutex_unlock(&transport->recv_mutex);
 
 	trace_rpc_socket_close(xprt, sock);
-	sock_release(sock);
+	fput(filp);
 
 	xprt_disconnect_done(xprt);
 }
@@ -1873,6 +1876,7 @@ static struct socket *xs_create_sock(struct rpc_xprt *xprt,
 		struct sock_xprt *transport, int family, int type,
 		int protocol, bool reuseport)
 {
+	struct file *filp;
 	struct socket *sock;
 	int err;
 
@@ -1893,6 +1897,11 @@ static struct socket *xs_create_sock(struct rpc_xprt *xprt,
 		goto out;
 	}
 
+	filp = sock_alloc_file(sock, O_NONBLOCK, NULL);
+	if (IS_ERR(filp))
+		return ERR_CAST(filp);
+	transport->file = filp;
+
 	return sock;
 out:
 	return ERR_PTR(err);
@@ -1938,6 +1947,7 @@ static int xs_local_finish_connecting(struct rpc_xprt *xprt,
 static int xs_local_setup_socket(struct sock_xprt *transport)
 {
 	struct rpc_xprt *xprt = &transport->xprt;
+	struct file *filp;
 	struct socket *sock;
 	int status = -EIO;
 
@@ -1950,6 +1960,13 @@ static int xs_local_setup_socket(struct sock_xprt *transport)
 	}
 	xs_reclassify_socket(AF_LOCAL, sock);
 
+	filp = sock_alloc_file(sock, O_NONBLOCK, NULL);
+	if (IS_ERR(filp)) {
+		status = PTR_ERR(filp);
+		goto out;
+	}
+	transport->file = filp;
+
 	dprintk("RPC:       worker connecting xprt %p via AF_LOCAL to %s\n",
 			xprt, xprt->address_strings[RPC_DISPLAY_ADDR]);