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Message-Id: <200808272037.49258.oliver@neukum.org>
Date: Wed, 27 Aug 2008 20:37:48 +0200
From: Oliver Neukum <oliver@...kum.org>
To: Alan Stern <stern@...land.harvard.edu>
Cc: Greg KH <greg@...ah.com>, linux-usb@...r.kernel.org,
Stefan Kopp <stefan_kopp@...lent.com>,
Marcel Janssen <korgull@...e.nl>,
Felipe Balbi <me@...ipebalbi.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: add USB test and measurement class driver - round 2
Am Mittwoch 27 August 2008 20:28:22 schrieb Alan Stern:
> On Wed, 27 Aug 2008, Greg KH wrote:
>
> > Here's an updated version of the usbtmc driver, with all of the
> > different issues that have been raised, hopefully addressed.
>
> This is an example of what I was discussing with Oliver. In all
> likelihood you simply don't need usbtmc_mutex, and using it will cause
> a lockdep violation.
>
> That's why so many of the other USB class drivers don't have an
> analogous static mutex.
>
> > +static int usbtmc_open(struct inode *inode, struct file *filp)
> > +{
> > + struct usb_interface *intf;
> > + struct usbtmc_device_data *data;
> > + int retval = -ENODEV;
> > +
> > + mutex_lock(&usbtmc_mutex);
>
> You must never acquire a lock in your open method if it will be held
> by your disconnect method while unregistering the minor.
And this rule depends on sharing the USB major or not. This needs
a big fat mention in Documentation.
Regards
Oliver
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