Re: [PATCH -next] xhci: fix two places when dealing with return value of function xhci_check_args

From: Mathias Nyman <mathias.nyman@linux.intel.com>
To: Hongyu Xie <xiehongyu1@kylinos.cn>, Greg KH <gregkh@linuxfoundation.org>
Cc: Hongyu Xie <xy521521@gmail.com>,
	mathias.nyman@intel.com, linux-kernel@vger.kernel.org,
	linux-usb@vger.kernel.org, 125707942@qq.com,
	stable@vger.kernel.org
Subject: Re: [PATCH -next] xhci: fix two places when dealing with return value of function xhci_check_args
Date: Thu, 27 Jan 2022 11:43:32 +0200	[thread overview]
Message-ID: <7af5b318-b1ac-0c74-1782-04ba50a3b5fa@linux.intel.com> (raw)
In-Reply-To: <e86972d3-e4a0-ad81-45ea-21137e3bfcb6@kylinos.cn>

On 26.1.2022 14.49, Hongyu Xie wrote:

>> Anyway, why is this unique to this one driver?  Why does it not show up
>> for any other driver?
> The whole thing is not about a particular driver. The thing is xhci_urb_enqueue shouldn't change the return value of xhci_check_args from -ENODEV to -EINVAL. Many other drivers only check if the return value of xchi_check_args is <= 0.

Agree, lets return -ENODEV when appropriate.

>>
>>> The whole point is, if xhci_check_args returns value A, xhci_urb_enqueque
>>> shouldn't return any
>>> other value, because that will change some driver's behavior(like r8152.c).
>> But you are changing how the code currently works.  Are you sure you
>> want to have this "succeed" if this is on a root hub?
> Yes, I'm changing how the code currently works but not on a root hub.
>>
>>> 2."So if 0 is returned, you will now return that here, is that ok?
>>> That is a change in functionality.
>>> But this can only ever be the case for a root hub, is that ok?"
>>>
>>> It's the same logic, but now xhci_urb_enqueue can return -ENODEV if xHC is
>>> halted.
>>> If it happens on a root hub,  xhci_urb_enqueue won't be called.
>>>
>>> 3."Again, this means all is good?  Why is this being called for a root hub?"
>>>
>>> It is the same logic with the old one, but now xhci_check_streams_endpoint
>>> can return -ENODEV if xHC is halted.
>> This still feels wrong to me, but I'll let the maintainer decide, as I
>> don't understand why a root hub is special here.
> 
> Thanks please. usb_submit_urb will call usb_hcd_submit_urb. And usb_hcd_submit_urb will call rh_urb_enqueue if it's on a root hub instead of calling hcd->driver->urb_enqueue(which is xhci_urb_enqueue in this case).

xhci_urb_enqueue() shouldn't be called for roothub urbs, but if it is then we
should continue to return -EINVAL 

xhci_check_args() should be rewritten later, but first we want a targeted fix
that can go to stable.

Your original patch would be ok after following modification:
if (ret <= 0)
	return ret ? ret : -EINVAL;

Thanks
-Mathias