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

Greg KH
2008-08-27T18:42:17Z

On Wed, Aug 27, 2008 at 02:28:22PM -0400, Alan Stern wrote:
> 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.

Ok, then it's just safe to drop this static mutex entirely, right?

> > +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?

Ah, yes, my fault, I converted this from using a private cdev to using
the usb_register_dev() call and forgot about this. Thanks for catching
it, I'll go fix this.

Oh, it's usb_deregister_dev(), stupid programmers with inconsitant
interfaces :)

thanks,

greg k-h