NFSv4: Fix callback server shutdown

We want to use kthread_stop() in order to ensure the threads are
shut down before we tear down the nfs_callback_info in nfs_callback_down.

Tested-and-reviewed-by: Kinglong Mee <kinglongmee@gmail.com>
Reported-by: Kinglong Mee <kinglongmee@gmail.com>
Fixes: bb6aeba736ba9 ("NFSv4.x: Switch to using svc_set_num_threads()...")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index c5e27eb..73a1f92 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -76,7 +76,10 @@ nfs4_callback_svc(void *vrqstp)
 
 	set_freezable();
 
-	while (!kthread_should_stop()) {
+	while (!kthread_freezable_should_stop(NULL)) {
+
+		if (signal_pending(current))
+			flush_signals(current);
 		/*
 		 * Listen for a request on the socket
 		 */
@@ -85,6 +88,8 @@ nfs4_callback_svc(void *vrqstp)
 			continue;
 		svc_process(rqstp);
 	}
+	svc_exit_thread(rqstp);
+	module_put_and_exit(0);
 	return 0;
 }
 
@@ -103,9 +108,10 @@ nfs41_callback_svc(void *vrqstp)
 
 	set_freezable();
 
-	while (!kthread_should_stop()) {
-		if (try_to_freeze())
-			continue;
+	while (!kthread_freezable_should_stop(NULL)) {
+
+		if (signal_pending(current))
+			flush_signals(current);
 
 		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
 		spin_lock_bh(&serv->sv_cb_lock);
@@ -121,11 +127,13 @@ nfs41_callback_svc(void *vrqstp)
 				error);
 		} else {
 			spin_unlock_bh(&serv->sv_cb_lock);
-			schedule();
+			if (!kthread_should_stop())
+				schedule();
 			finish_wait(&serv->sv_cb_waitq, &wq);
 		}
-		flush_signals(current);
 	}
+	svc_exit_thread(rqstp);
+	module_put_and_exit(0);
 	return 0;
 }
 
@@ -221,14 +229,14 @@ static int nfs_callback_up_net(int minorversion, struct svc_serv *serv,
 static struct svc_serv_ops nfs40_cb_sv_ops = {
 	.svo_function		= nfs4_callback_svc,
 	.svo_enqueue_xprt	= svc_xprt_do_enqueue,
-	.svo_setup		= svc_set_num_threads,
+	.svo_setup		= svc_set_num_threads_sync,
 	.svo_module		= THIS_MODULE,
 };
 #if defined(CONFIG_NFS_V4_1)
 static struct svc_serv_ops nfs41_cb_sv_ops = {
 	.svo_function		= nfs41_callback_svc,
 	.svo_enqueue_xprt	= svc_xprt_do_enqueue,
-	.svo_setup		= svc_set_num_threads,
+	.svo_setup		= svc_set_num_threads_sync,
 	.svo_module		= THIS_MODULE,
 };