linux-kernel - Re: [PATCH] USB testing driver: convert dev->sem to mutex

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Message-Id: <1196795342.1568.41.camel@jnielson-xp.ddns.mvista.com>
Date:	Tue, 04 Dec 2007 11:09:02 -0800
From:	Daniel Walker <dwalker@...sta.com>
To:	Matthias Kaehlcke <matthias.kaehlcke@...il.com>
Cc:	gregkh@...e.de, linux-usb-users@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu
Subject: Re: [PATCH] USB testing driver: convert dev->sem to mutex

On Tue, 2007-12-04 at 17:55 +0100, Matthias Kaehlcke wrote:
> @@ -1990,7 +1991,7 @@ static void usbtest_disconnect (struct
> usb_interface *intf)
>  {
>         struct usbtest_dev      *dev = usb_get_intfdata (intf);
>  
> -       down (&dev->sem);
> +       mutex_lock(&dev->lock);
>  
>         usb_set_intfdata (intf, NULL);
>         dev_dbg (&intf->dev, "disconnect\n"); 

This looks like a bit of an anomaly.. The code that isn't shown above is
the "kfree(dev)" .. So this isn't legal since it's freeing a locked
mutex. Here's a excerpt from the comment above mutex_lock(),

 * The mutex must later on be released by the same task that
 * acquired it. Recursive locking is not allowed. The task
 * may not exit without first unlocking the mutex. Also, kernel
 * memory where the mutex resides mutex must not be freed with
 * the mutex still locked. The mutex must first be initialized
 * (or statically defined) before it can be locked. memset()-ing
 * the mutex to 0 is not allowed.

Daniel

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