Bluetooth: bnep: Fix module reference

We cannot call module_put(THIS_MODULE) if this is our last reference. Otherwise,
this call may cleanup our module before it returns.

Gladly, the kthread API provides a simple wrapper for us. So lets use
module_put_and_exit() to avoid a race condition with the module cleanup code.
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

net/bluetooth/bnep/core.c

@@ -79,17 +79,12 @@ static struct bnep_session *__bnep_get_session(u8 *dst)
 
 static void __bnep_link_session(struct bnep_session *s)
 {
-	/* It's safe to call __module_get() here because sessions are added
-	   by the socket layer which has to hold the reference to this module.
-	 */
-	__module_get(THIS_MODULE);
 	list_add(&s->list, &bnep_session_list);
 }
 
 static void __bnep_unlink_session(struct bnep_session *s)
 {
 	list_del(&s->list);
-	module_put(THIS_MODULE);
 }
 
 static int bnep_send(struct bnep_session *s, void *data, size_t len)
@@ -530,6 +525,7 @@ static int bnep_session(void *arg)
 
 	up_write(&bnep_session_sem);
 	free_netdev(dev);
+	module_put_and_exit(0);
 	return 0;
 }
 
@@ -616,9 +612,11 @@ int bnep_add_connection(struct bnep_connadd_req *req, struct socket *sock)
 
 	__bnep_link_session(s);
 
+	__module_get(THIS_MODULE);
 	s->task = kthread_run(bnep_session, s, "kbnepd %s", dev->name);
 	if (IS_ERR(s->task)) {
 		/* Session thread start failed, gotta cleanup. */
+		module_put(THIS_MODULE);
 		unregister_netdev(dev);
 		__bnep_unlink_session(s);
 		err = PTR_ERR(s->task);