Date: Mon, 23 Nov 2015 15:40:31 +0800
From: Peter Chen <peter.chen@freescale.com>
To: Alan Stern <stern@rowland.harvard.edu>
CC: Marek Szyprowski <m.szyprowski@samsung.com>, <linux-usb@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>,
        Ruslan Bilovol <ruslan.bilovol@gmail.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH v6 4/4] usb: gadget: udc-core: independent registration
 of gadgets and gadget drivers
Message-ID: <20151123074030.GC16321@shlinux2>
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On Fri, Nov 20, 2015 at 11:27:36AM -0500, Alan Stern wrote:
> On Fri, 20 Nov 2015, Marek Szyprowski wrote:
> 
> > From: Ruslan Bilovol <ruslan.bilovol@gmail.com>
> > 
> > Change behavior during registration of gadgets and
> > gadget drivers in udc-core. Instead of previous
> > approach when for successful probe of usb gadget driver
> > at least one usb gadget should be already registered
> > use another one where gadget drivers and gadgets
> > can be registered in udc-core independently.
> > 
> > Independent registration of gadgets and gadget drivers
> > is useful for built-in into kernel gadget and gadget
> > driver case - because it's possible that gadget is
> > really probed only on late_init stage (due to deferred
> > probe) whereas gadget driver's probe is silently failed
> > on module_init stage due to no any UDC added.
> > 
> > Also it is useful for modules case - now there is no
> > difference what module to insert first: gadget module
> > or gadget driver one.
> > 
> > Tested-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
> > [simplified code as requested by Alan Stern and Felipe Balbi]
> > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> 
> ...
> 
> > @@ -475,9 +492,16 @@ void usb_del_gadget_udc(struct usb_gadget *gadget)
> >  	list_del(&udc->list);
> >  	mutex_unlock(&udc_lock);
> >  
> > -	if (udc->driver)
> > +	if (udc->driver) {
> > +		struct usb_gadget_driver *driver = udc->driver;
> > +
> >  		usb_gadget_remove_driver(udc);
> >  
> > +		mutex_lock(&udc_lock);
> > +		list_add(&driver->pending, &gadget_driver_pending_list);
> > +		mutex_unlock(&udc_lock);
> > +	}
> 
> It looks like there is a race here with usb_gadget_unregister_driver().  
> Would it be okay to hold the udc_lock mutex throughout the whole "if"  
> statement?
> 

+1

In fact, only one mutex_lock/mutex_unlock is needed at this function.
-- 

Best Regards,
Peter Chen
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