Re: [PATCH 4/4] usb: libusual: locking cleanup

Pete Zaitcev
2007-12-22T06:26:22Z

On Fri, 21 Dec 2007 00:00:04 -0800, Daniel Walker <dwalker@mvista.com> wrote:

> I converted the usu_init_notify semaphore to normal mutex usage, and it
> should still prevent the request_module before the init routine is
> complete. Before it acted more like a complete, now the mutex protects
> two distinct section from running at the same time..

Let's see.

> @@ -178,10 +179,7 @@ static int usu_probe_thread(void *arg)
> int rc;
> unsigned long flags;
>
> - /* A completion does not work here because it's counted. */
> - down(&usu_init_notify);
> - up(&usu_init_notify);
> -
> + mutex_lock(&usu_probe_mutex);
> rc = request_module(bias_names[type]);

When I tried it, usb-storage would not load with unresolved symbols.
It happens if child (usu_probe_thread) runs ahead of its parent
(usb_usual_init -> usb_register -> usu_probe). It's entirely possible,
depending on your scheduler.

I hate this down-up trick too, so if you have a better idea, I'm all ears.

-- Pete