NFSv4.x: Fix up the global tracking of the callback server

Ensure that the nfs_callback_info[] array correctly tracks the
struct svc_serv.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/callback.c

@@ -201,7 +201,6 @@ static int nfs_callback_start_svc(int minorversion, struct rpc_xprt *xprt,
 
 	svc_sock_update_bufs(serv);
 
-	cb_info->serv = serv;
 	cb_info->rqst = rqstp;
 	cb_info->task = kthread_create(serv->sv_ops->svo_function,
 				    cb_info->rqst,
@@ -300,7 +299,7 @@ static struct svc_serv *nfs_callback_create_svc(int minorversion)
 	/*
 	 * Check whether we're already up and running.
 	 */
-	if (cb_info->task) {
+	if (cb_info->serv) {
 		/*
 		 * Note: increase service usage, because later in case of error
 		 * svc_destroy() will be called.
@@ -333,6 +332,7 @@ static struct svc_serv *nfs_callback_create_svc(int minorversion)
 		printk(KERN_ERR "nfs_callback_create_svc: create service failed\n");
 		return ERR_PTR(-ENOMEM);
 	}
+	cb_info->serv = serv;
 	/* As there is only one thread we need to over-ride the
 	 * default maximum of 80 connections
 	 */
@@ -375,6 +375,8 @@ int nfs_callback_up(u32 minorversion, struct rpc_xprt *xprt)
 	 * thread exits.
 	 */
 err_net:
+	if (!cb_info->users)
+		cb_info->serv = NULL;
 	svc_destroy(serv);
 err_create:
 	mutex_unlock(&nfs_callback_mutex);
@@ -396,9 +398,11 @@ void nfs_callback_down(int minorversion, struct net *net)
 	mutex_lock(&nfs_callback_mutex);
 	nfs_callback_down_net(minorversion, cb_info->serv, net);
 	cb_info->users--;
-	if (cb_info->users == 0 && cb_info->task != NULL) {
-		kthread_stop(cb_info->task);
-		dprintk("nfs_callback_down: service stopped\n");
+	if (cb_info->users == 0) {
+		if (cb_info->task != NULL) {
+			kthread_stop(cb_info->task);
+			dprintk("nfs_callback_down: service stopped\n");
+		}
 		svc_exit_thread(cb_info->rqst);
 		dprintk("nfs_callback_down: service destroyed\n");
 		cb_info->serv = NULL;