On Wed, Jul 09, 2003 at 04:18:25PM -0400, Alan Stern wrote:
> On Wed, 9 Jul 2003, Greg KH wrote:
>
> > On Mon, Jul 07, 2003 at 10:20:32AM -0400, Alan Stern wrote:
> > > Greg:
> > >
> > > This fixes a minor error in usb-skeleton's disconnect() routine: if the
> > > interface's private data is NULL, the current code exits without releasing
> > > the disconnect_sem semaphore.
> >
> > Yeah, but if dev is null, then the semaphore is already released, right?
>
> Wrong. Here's an extract from the current version of the code:
>
> static void skel_disconnect(struct usb_interface *interface)
> {
> struct usb_skel *dev;
> int minor;
>
> /* prevent races with open() */
> down (&disconnect_sem);
>
> dev = usb_get_intfdata (interface);
> usb_set_intfdata (interface, NULL);
>
> if (!dev)
> return;
>
> As you can see, disconnect_sem is acquired but not released if dev is
> NULL.
Ah yes, that is a problem.
> > So yes, the check is being paranoid, but I don't see a problem with
> > being paranoid in this kind of situation, do you?
>
> Well, I sort of do. If the pointer really can never be NULL, then it
> doesn't make much difference whether or not you check; the difference is
> code size and speed is completely negligible. There is a difference in
> clarity though. Seeing that check makes me wonder, "What's that doing
> there? How could the pointer ever be NULL? Is someone just being
> paranoid or can that really happen?" I don't like that kind of
> distraction when trying to read code.
I am tending to agree with you there. Ok, I'll go add your patch to my
todo list of things I need to get off my butt and apply (been busy these
past few days, working on a talk, and now am at a conference...)
thanks,
greg k-h
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