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    SubjectRe: [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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