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

Andrew Morton
2007-12-22T04:24:53Z

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..
>
> Signed-off-by: Daniel Walker <dwalker@mvista.com>
>
> ---
> drivers/usb/storage/libusual.c | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> Index: linux-2.6.23/drivers/usb/storage/libusual.c
> ===================================================================
> --- linux-2.6.23.orig/drivers/usb/storage/libusual.c
> +++ linux-2.6.23/drivers/usb/storage/libusual.c
> @@ -9,6 +9,7 @@
> #include <linux/usb_usual.h>
> #include <linux/vmalloc.h>
> #include <linux/kthread.h>
> +#include <linux/mutex.h>
>
> /*
> */
> @@ -30,7 +31,7 @@ static atomic_t usu_bias = ATOMIC_INIT(U
> #define BIAS_NAME_SIZE (sizeof("usb-storage"))
> static const char *bias_names[3] = { "none", "usb-storage", "ub" };
>
> -static struct semaphore usu_init_notify;
> +static DEFINE_MUTEX(usu_probe_mutex);
> static DECLARE_COMPLETION(usu_end_notify);
> static atomic_t total_threads = ATOMIC_INIT(0);
>
> @@ -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]);
> spin_lock_irqsave(&usu_lock, flags);
> if (rc == 0 && (st->fls & USU_MOD_FL_PRESENT) == 0) {
> @@ -194,6 +192,7 @@ static int usu_probe_thread(void *arg)
> }
> st->fls &= ~USU_MOD_FL_THREAD;
> spin_unlock_irqrestore(&usu_lock, flags);
> + mutex_unlock(&usu_probe_mutex);
>
> complete_and_exit(&usu_end_notify, 0);
> }
> @@ -204,10 +203,9 @@ static int __init usb_usual_init(void)
> {
> int rc;
>
> - sema_init(&usu_init_notify, 0);
> -
> + mutex_lock(&usu_probe_mutex);
> rc = usb_register(&usu_driver);
> - up(&usu_init_notify);
> + mutex_unlock(&usu_probe_mutex);
> return rc;
> }

That's some pretty hairy-looking code you're playing with there. Has this
been runtime tested?