On Thu, 2012-03-15 at 19:42 +0800, Ming Lei wrote:
> Hi,
>
> On Thu, Mar 15, 2012 at 7:31 PM, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
>
> >> So how about using lockdep_set_class to address the problem?
> >
> > Can do, you say the USB spec allows for 32 interfaces, what happens if a
> > device manufacturer 'mis-reads' the spec and puts 64 on? Will that
> > simply not work or will we get 'fun' results?
>
> USB spec only says that "Each configuration has one or more interfaces
> and each interface has zero or more endpoints. "[1] In fact, maybe 255
> interfaces can be described in configuration desc. I mean that current
> USB protocol stack(usbcore) only supports 32 interfaces in one
> configuration, see below:
>
> #define USB_MAXINTERFACES 32
> struct usb_host_config {
> ......
> struct usb_interface *interface[USB_MAXINTERFACES];
> ......
> }
OK, so I guess our USB stack will fall over before lockdep does.
Sure add something like:
struct lock_class_key usb_interface_key[USB_MAXINTERFACES];
and add something like:
mutex_init(&us->dev_mutex);
+ lockdep_set_class(&us->dev_mutex, &usb_interface_key[if]);
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