linux-kernel - Re: [PATCHv3 5/5] usb: gadget: udc-core: independent registration of gadgets and gadget drivers

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Date:	Tue, 10 Mar 2015 21:31:39 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ruslan Bilovol <ruslan.bilovol@...il.com>
cc:	"Balbi, Felipe" <balbi@...com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Krzysztof Opasiak <k.opasiak@...sung.com>,
	Peter Chen <peter.chen@...escale.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	Andrzej Pietrasiewicz <andrzej.p@...sung.com>
Subject: Re: [PATCHv3 5/5] usb: gadget: udc-core: independent registration
 of gadgets and gadget drivers

On Wed, 11 Mar 2015, Ruslan Bilovol wrote:

> Hi Alan,

Hello.

> > If you add the list_init and list_del_init above, this loop won't be
> > needed.  You can just call list_del.
> 
> I disagree with this. This function is externally visible and we can't
> guarantee that some buggy code will not call it with uninitialized
> 'pending' list_head. For example, if it never called usb_gadget_probe_driver()
> but calls usb_gadget_unregister_driver().
> As per my opinion it's better to check it and return -ENODEV rather than
> fail on deleting of uninitialized list_head. In this case adding the list_init
> and list_del_init above is not needed.

No, that is not the approach used in the rest of the kernel.  We _want_
to know about bugs, so we can fix them.  If you silently return -ENODEV
then nobody will realize anything is wrong, but a big fat WARN or OOPS
caused by an uninitialized list_head will draw people's attention very
quickly.

Alan Stern

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