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

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Message-ID: <Pine.LNX.4.44L0.1511241027200.1803-100000@iolanthe.rowland.org>
Date:	Tue, 24 Nov 2015 10:53:33 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Peter Chen <peter.chen@...escale.com>
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 Tue, 24 Nov 2015, Peter Chen wrote:

> > > @@ -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?

On Tue, 24 Nov 2015, Marek Szyprowski wrote:

> 'pending' handle is added to gadget_driver_pending_list in
> usb_gadget_probe_driver(),
> then when udc is available it is removed from this list and bound to the
> given driver.
> In usb_gadget_unregister_driver() the gadget is either unbound from the
> udc or if is
> was not bound to any udc, removed from pending list. I see no need for
> adding
> INIT_LIST_HEAD.

I'm sorry, you guys are right.  I didn't notice the "if (ret) {" line
added to usb_gadget_unregister_driver().  That line insures that we
don't try to remove the driver from the pending list unless it really
is on the list.

So never mind...

Alan Stern

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