Bluetooth: cmtp: 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/cmtp/core.c

@@ -67,14 +67,12 @@ static struct cmtp_session *__cmtp_get_session(bdaddr_t *bdaddr)
 
 static void __cmtp_link_session(struct cmtp_session *session)
 {
-	__module_get(THIS_MODULE);
 	list_add(&session->list, &cmtp_session_list);
 }
 
 static void __cmtp_unlink_session(struct cmtp_session *session)
 {
 	list_del(&session->list);
-	module_put(THIS_MODULE);
 }
 
 static void __cmtp_copy_session(struct cmtp_session *session, struct cmtp_conninfo *ci)
@@ -327,6 +325,7 @@ static int cmtp_session(void *arg)
 	up_write(&cmtp_session_sem);
 
 	kfree(session);
+	module_put_and_exit(0);
 	return 0;
 }
 
@@ -376,9 +375,11 @@ int cmtp_add_connection(struct cmtp_connadd_req *req, struct socket *sock)
 
 	__cmtp_link_session(session);
 
+	__module_get(THIS_MODULE);
 	session->task = kthread_run(cmtp_session, session, "kcmtpd_ctr_%d",
 								session->num);
 	if (IS_ERR(session->task)) {
+		module_put(THIS_MODULE);
 		err = PTR_ERR(session->task);
 		goto unlink;
 	}