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

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
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