Re: [PATCH] USB: add USB test and measurement class driver - round 2

Alan Stern
2008-08-27T18:28:36Z

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