linux-kernel - Re: [PATCH v6 4/4] usb: gadget: udc-core: independent registration of gadgets and gadget drivers

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Message-ID: <Pine.LNX.4.44L0.1511201120290.1647-100000@iolanthe.rowland.org>
Date:	Fri, 20 Nov 2015 11:27:36 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
cc:	linux-usb@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	Ruslan Bilovol <ruslan.bilovol@...il.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v6 4/4] usb: gadget: udc-core: independent registration
 of gadgets and gadget drivers

On Fri, 20 Nov 2015, Marek Szyprowski wrote:

> From: Ruslan Bilovol <ruslan.bilovol@...il.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@...e-electrons.com>
> Signed-off-by: Ruslan Bilovol <ruslan.bilovol@...il.com>
> [simplified code as requested by Alan Stern and Felipe Balbi]
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.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?

Alan Stern

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