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

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Message-ID: <7af5b318-b1ac-0c74-1782-04ba50a3b5fa@linux.intel.com>
Date:   Thu, 27 Jan 2022 11:43:32 +0200
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Hongyu Xie <xiehongyu1@...inos.cn>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     Hongyu Xie <xy521521@...il.com>, mathias.nyman@...el.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        125707942@...com, stable@...r.kernel.org
Subject: Re: [PATCH -next] xhci: fix two places when dealing with return value
 of function xhci_check_args

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