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Message-ID: <Pine.LNX.4.44L0.0808271423030.17568-100000@iolanthe.rowland.org>
Date: Wed, 27 Aug 2008 14:28:22 -0400 (EDT)
From: Alan Stern <stern@...land.harvard.edu>
To: Greg KH <greg@...ah.com>
cc: Oliver Neukum <oliver@...kum.org>, <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
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.
> +static int usbtmc_probe(struct usb_interface *intf,
> + const struct usb_device_id *id)
> +{
...
> + retcode = usb_register_dev(intf, &usbtmc_class);
> + if (retcode) {
> + dev_err(&intf->dev, "Not able to get a minor"
> + " (base %u, slice default): %d\n", USBTMC_MINOR_BASE,
> + retcode);
> + goto error_register;
> + }
> + dev_dbg(&intf->dev, "Using minor number %d\n", intf->minor);
You do call usb_register_dev() during probe...
> +
> + return 0;
> +
> +error_register:
> + sysfs_remove_group(&intf->dev.kobj, &capability_attr_grp);
> + sysfs_remove_group(&intf->dev.kobj, &data_attr_grp);
> + kref_put(&data->kref, usbtmc_delete);
> + return retcode;
> +}
> +
> +static void usbtmc_disconnect(struct usb_interface *intf)
> +{
> + struct usbtmc_device_data *data;
> +
> + dev_dbg(&intf->dev, "usbtmc_disconnect called\n");
> +
> + mutex_lock(&usbtmc_mutex);
> + data = usb_get_intfdata(intf);
> + sysfs_remove_group(&intf->dev.kobj, &capability_attr_grp);
> + sysfs_remove_group(&intf->dev.kobj, &data_attr_grp);
> + kref_put(&data->kref, usbtmc_delete);
> + mutex_unlock(&usbtmc_mutex);
> +}
But you don't call usb_unregister_dev() during disconnect. An
oversight?
Alan Stern
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