Re: [PATCH] usb: gadget: composite: unlock spinlock before usb_gadget_disconnect()

[Felipe Balbi]

On Fri, Jun 13, 2014 at 11:36:24AM +0000, David Laight wrote:
> From: Robert Baldyga
> > usb_gadget_disconnect() shouldn't be called under spinlock to avoid
> > spinlock recursion. Function usb_gadget_disconnect() calls pullup(),
> > which is callback from UDC driver, usually calling composite_disconnect().
> > This function wants to lock spinlock used in usb_function_deactivate()
> > causing spinlock recursion.
> ...
> > +++ b/drivers/usb/gadget/composite.c
> > @@ -260,8 +260,11 @@ int usb_function_deactivate(struct usb_function *function)
> > 
> >  	spin_lock_irqsave(&cdev->lock, flags);
> > 
> > -	if (cdev->deactivations == 0)
> > +	if (cdev->deactivations == 0) {
> > +		spin_unlock_irqrestore(&cdev->lock, flags);
> >  		status = usb_gadget_disconnect(cdev->gadget);
> > +		spin_lock_irqsave(&cdev->lock, flags);
> > +	}
> >  	if (status == 0)
> >  		cdev->deactivations++;
> 
> That sort of change rings big alarm bells.
> You've effectively isolated the usb_gadget_disconnect() call
> from the check that cdev->deactivations == 0.
> And then you increment cdev->deactivations below.
> 
> Looks like it will be racy to me.

yes, it will. Fixing this requires a much more involved change.

-- 
balbi

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