usb: cdc_acm: Do not leak URB buffers

[Oliver Neukum <oneukum@suse.com>]

On Mo, 2018-09-24 at 10:20 +0200, Romain Izard wrote:
> 2018-09-21 15:27 +0200, Oliver Neukum <oneukum@suse.com>:
> > 
> > On Do, 2018-09-20 at 16:49 +0200, Romain Izard wrote:
> > > When the ACM TTY port is disconnected, the URBs it uses must be killed,
> > > and then the buffers must be freed. Unfortunately a previous refactor
> > > removed the code freeing the buffers because it looked extremely similar
> > > to the code killing the URBs.
> > > 
> > > As a result, there were many new leaks for each plug/unplug cycle of a
> > > CDC-ACM device, that were detected by kmemleak.
> > > 
> > > Restore the missing code, and the memory leak is removed.
> > 
> > Try as i may, I don't see the difference. Could you put a comment exactly
> > describing the issue into the code itself, lest this problem reappear?
> > 
> 
> The critical point is that on shutdown, the URBs need to be killed with
> usb_kill_urb, and then released with usb_free_urb.
> 
> As the code for iterating on all allocated URBs and the parameters are the
> same for both functions, which also have the same length, the difference is
> visually subtle. But conceptually, it is not subtle at all.
> 
> I believe that this does not need a comment.

Damn. I am blind.

	Regards
		Oliver