Add a reference to sunrpc in svc_addsock

The svc_addsock function adds transport instances without taking a
reference on the sunrpc.ko module, however, the generic transport
destruction code drops a reference when a transport instance
is destroyed.

Add a try_module_get call to the svc_addsock function for transport
instances added by this function.
Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Tested-by: Jeff Moyer <jmoyer@redhat.com>

net/sunrpc/svcsock.c

@@ -1183,7 +1183,11 @@ int svc_addsock(struct svc_serv *serv,
 	else if (so->state > SS_UNCONNECTED)
 		err = -EISCONN;
 	else {
-		svsk = svc_setup_socket(serv, so, &err, SVC_SOCK_DEFAULTS);
+		if (!try_module_get(THIS_MODULE))
+			err = -ENOENT;
+		else
+			svsk = svc_setup_socket(serv, so, &err,
+						SVC_SOCK_DEFAULTS);
 		if (svsk) {
 			struct sockaddr_storage addr;
 			struct sockaddr *sin = (struct sockaddr *)&addr;
@@ -1196,7 +1200,8 @@ int svc_addsock(struct svc_serv *serv,
 			spin_unlock_bh(&serv->sv_lock);
 			svc_xprt_received(&svsk->sk_xprt);
 			err = 0;
-		}
+		} else
+			module_put(THIS_MODULE);
 	}
 	if (err) {
 		sockfd_put(so);