linux-kernel - Re: [PATCH] usb: gadget: udc-core: call udc

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Date:	Mon, 15 Dec 2014 11:14:55 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Robert Baldyga <r.baldyga@...sung.com>
cc:	balbi@...com, <gregkh@...uxfoundation.org>,
	<peter.chen@...escale.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <m.szyprowski@...sung.com>,
	<k.opasiak@...sung.com>
Subject: Re: [PATCH] usb: gadget: udc-core: call udc_stop() before gadget
 unbind

On Fri, 12 Dec 2014, Robert Baldyga wrote:

> As usb function drivers assumes that all usb request will be completed
> before function unbind call, we should supply such behavior. In some
> cases ep_disable() won't kill all request effectively, because some
> IN requests can be in running state. In such situation it's possible
> to have unbind function called before last request completion, which
> can cause problems.
> 
> For example unbinding f_ecm function while request on 'notify' endpoint
> is not completed, ends up NULL pointer dereference in unbind() function.
> 
> usb_gadget_udc_stop() call causes completion of all requests so if it's
> called before gadget unbind there is no risk that some of requests will
> stay uncompleted.
> 
> Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>
> ---
>  drivers/usb/gadget/udc/udc-core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/udc/udc-core.c b/drivers/usb/gadget/udc/udc-core.c
> index e31d574..6f0d233 100644
> --- a/drivers/usb/gadget/udc/udc-core.c
> +++ b/drivers/usb/gadget/udc/udc-core.c
> @@ -331,8 +331,8 @@ static void usb_gadget_remove_driver(struct usb_udc *udc)
>  
>  	usb_gadget_disconnect(udc->gadget);
>  	udc->driver->disconnect(udc->gadget);
> -	udc->driver->unbind(udc->gadget);
>  	usb_gadget_udc_stop(udc);
> +	udc->driver->unbind(udc->gadget);
>  
>  	udc->driver = NULL;
>  	udc->dev.driver = NULL;

There has been a lot of churn and a lot of bug fixes involving those
lines of code.  Have you checked the git log for this function?  It's
quite possible that interchanging those two statements will recreate a
bug that has already been fixed.

Alan Stern

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