On Wed, 5 Apr 2017, Felipe Balbi wrote:
> >> >> --- a/drivers/usb/gadget/udc/core.c
> >> >> +++ b/drivers/usb/gadget/udc/core.c
> >> >> @@ -1273,6 +1273,7 @@ void usb_del_gadget_udc(struct usb_gadget *gadget)
> >> >> flush_work(&gadget->work);
> >> >> device_unregister(&udc->dev);
> >> >> device_unregister(&gadget->dev);
> >> >> + memset(&gadget->dev, 0x00, sizeof(gadget->dev));
> >> >> }
> >> >> EXPORT_SYMBOL_GPL(usb_del_gadget_udc);
> >> >
> >> > Isn't this dangerous? It's quite possible that the device_unregister()
> >>
> >> not on the gadget API, no.
> >>
> >> > call on the previous line invokes the gadget->dev.release callback,
> >> > which might deallocate gadget. If that happens, your new memset will
> >> > oops.
> >>
> >> that won't happen. struct usb_gadget is a member of the UDC's private
> >> structure, like this:
> >>
> >> struct dwc3 {
> >> [...]
> >> struct usb_gadget gadget;
> >> struct usb_gadget_driver *gadget_driver;
> >> [...]
> >> };
> >
> > Yes. So what? Can't the UDC driver use the refcount inside struct
> > usb_gadget to control the lifetime of its private structure?
>
> nope, not being used. At least not yet.
I'm not convinced (yet)...
> > (By the way, can you tell what's going on in net2280.c? I must be
> > missing something; it looks like gadget_release() would quickly run
> > into problems because it calls dev_get_drvdata() for &gadget->dev, but
> > net2280_probe() never calls dev_set_drvdata() for that device.
> > Furthermore, net2280_remove() continues to reference the net2280 struct
> > after calling usb_del_gadget_udc(), and it never does seem to do a
> > final put.)
>
> static int net2280_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> {
> struct net2280 *dev;
> unsigned long resource, len;
> void __iomem *base = NULL;
> int retval, i;
>
> /* alloc, and start init */
> dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> if (dev == NULL) {
> retval = -ENOMEM;
> goto done;
> }
>
> pci_set_drvdata(pdev, dev);
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^
That sets the driver data in the struct pci_dev, not in
dev->gadget.dev. As far as I can see, _nothing_ in the driver sets the
driver data in dev->gadget.dev.
(Even after all these years, I still get bothered by the way Dave
Brownell used to call everything "dev"... IIRC, at one time he had a
line of code that went something like: dev->dev.dev = &pdev->dev !)
> >> I'm actually thinking that struct usb_gadget shouldn't have a struct
> >> device at all. Just a pointer to a device, that would solve all these
> >> issues.
> >
> > A pointer to which device? The UDC? That would change the directory
> > layout in sysfs.
>
> indeed. Would that be a problem?
Possibly for some userspace tool.
> > Or a pointer to a separate dynamically allocated device (the way struct
> > usb_hcd contains a pointer to the root hub device)? That would work.
> > If the UDC driver wanted to re-register the gadget, it would have to
> > allocate a new device.
>
> That could be done as well, if maintaining the directory structure is a
> must.
Alan Stern
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