# Re: \[PATCH\] net/usbnet: avoid recursive locking in usbnet\_stop()

- From: Alan Stern \<hidden\>
- Date: 2012-02-20 21:40:49 
- List: netdev
- Page: https://ratatoskr.run/netdev/2012/02/10889078

```text
On Mon, 20 Feb 2012, Sebastian Andrzej Siewior wrote:

> > What's the issue here?
> >
> > If a driver calls usb_unlink_urb() while holding a lock, and the
> > completion routine tries to acquire the same lock, then deadlock is
> > possible.  The fact that usb_unlink_urb() is asynchronous is not a
> > guarantee of anything; the HCD is allowed to call the completion
> > handler from within usb_unlink_urb().
> >
> > It's true that the kerneldoc for usb_unlink_urb() says "This request is
> > always asynchronous".  It might be a good idea to remove the word
> > "always", because it seems to give people the wrong idea.
> 
> I see. So you approve that patch and suggest to remove the "always"
> wording plus adding something like "the hcd might call complete routine
> during unlink" ?

Well, I haven't read the patch and don't really understand what issue 
it tries to solve.  But if that issue is the one I talked about above 
then yes, it makes sense.  And changing the documentation as you 
suggest would be a good thing to do in any case.

Alan Stern

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