NFSd: set nfsd_serv to NULL after service destruction

In nfsd_destroy():

	if (destroy)
		svc_shutdown_net(nfsd_serv, net);
	svc_destroy(nfsd_server);

svc_shutdown_net(nfsd_serv, net) calls nfsd_last_thread(), which sets
nfsd_serv to NULL, causing a NULL dereference on the following line.
Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfsd.h

@@ -82,6 +82,8 @@ static inline void nfsd_destroy(struct net *net)
 	if (destroy)
 		svc_shutdown_net(nfsd_serv, net);
 	svc_destroy(nfsd_serv);
+	if (destroy)
+		nfsd_serv = NULL;
 }
 
 #if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)

fs/nfsd/nfssvc.c

@@ -254,8 +254,6 @@ static void nfsd_shutdown(void)
 
 static void nfsd_last_thread(struct svc_serv *serv, struct net *net)
 {
-	/* When last nfsd thread exits we need to do some clean-up */
-	nfsd_serv = NULL;
 	nfsd_shutdown();
 
 	svc_rpcb_cleanup(serv, net);
@@ -332,6 +330,7 @@ static int nfsd_get_default_max_blksize(void)
 int nfsd_create_serv(void)
 {
 	int error;
+	struct net *net = current->nsproxy->net_ns;
 
 	WARN_ON(!mutex_is_locked(&nfsd_mutex));
 	if (nfsd_serv) {
@@ -346,7 +345,7 @@ int nfsd_create_serv(void)
 	if (nfsd_serv == NULL)
 		return -ENOMEM;
 
-	error = svc_bind(nfsd_serv, current->nsproxy->net_ns);
+	error = svc_bind(nfsd_serv, net);
 	if (error < 0) {
 		svc_destroy(nfsd_serv);
 		return error;
@@ -557,12 +556,13 @@ nfsd(void *vrqstp)
 	nfsdstats.th_cnt --;
 
 out:
-	if (rqstp->rq_server->sv_nrthreads == 1)
-		svc_shutdown_net(rqstp->rq_server, &init_net);
+	rqstp->rq_server = NULL;
 
 	/* Release the thread */
 	svc_exit_thread(rqstp);
 
+	nfsd_destroy(&init_net);
+
 	/* Release module */
 	mutex_unlock(&nfsd_mutex);
 	module_put_and_exit(0);