linux-kernel - Re: [PATCH v7 4/4] usb: gadget: udc-core: independent registration of gadgets and gadget drivers

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Message-ID: <20151124022449.GA25698@shlinux2>
Date:	Tue, 24 Nov 2015 10:24:50 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Marek Szyprowski <m.szyprowski@...sung.com>,
	<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 v7 4/4] usb: gadget: udc-core: independent registration
 of gadgets and gadget drivers

On Mon, Nov 23, 2015 at 10:32:53AM -0500, Alan Stern wrote:
> On Mon, 23 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,
> >  fixed checkpatch issues]
> > Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > Tested-by: Peter Chen <peter.chen@...escale.com>
> 
> I missed this the last time through...
> 
> > @@ -403,6 +408,18 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
> >  	usb_gadget_set_state(gadget, USB_STATE_NOTATTACHED);
> >  	udc->vbus = true;
> >  
> > +	/* pick up one of pending gadget drivers */
> > +	list_for_each_entry(driver, &gadget_driver_pending_list, pending) {
> > +		if (!driver->udc_name || strcmp(driver->udc_name,
> > +						dev_name(&udc->dev)) == 0) {
> > +			ret = udc_bind_to_driver(udc, driver);
> > +			if (ret)
> > +				goto err4;
> > +			list_del(&driver->pending);
> 
> This has to be list_del_init().  And somewhere in
> usb_gadget_probe_driver() you need to do
> INIT_LIST_HEAD(&driver->pending).
> 
> > @@ -577,6 +596,10 @@ int usb_gadget_unregister_driver(struct usb_gadget_driver *driver)
> >  			break;
> >  		}
> >  
> > +	if (ret) {
> > +		list_del(&driver->pending);
> 
> Otherwise this will cause a crash or corrupt some random area of 
> memory.
> 

Alan, would you please explain more what use case will cause memory
corruption for above code?

-- 

Best Regards,
Peter Chen
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