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

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Date:   Fri, 28 Jan 2022 11:48:34 +0800
From:   谢泓宇 <xiehongyu1@...inos.cn>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        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

Hi Mathias,

On 2022/1/27 17:43, Mathias Nyman wrote:
> 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_urb_enqueue() won't be called for roothub urbs, only for none 
roothub urbs(see usb_hcd_submit_urb()).

So xhci_urb_enqueue() will not get 0 from xhci_check_args().

Still return -EINVAL if xhci_check_args() returns 0 in xhci_urb_enqueue()?

>
> 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;

I have two questions:

     1) Why return -EINVAL for roothub urbs?

     2) Should I change all the return statements about 
xhci_check_args() in drivers/usb/host/xhci.c?

     There are 6 of them.

>
> Thanks
> -Mathias