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

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Message-ID: <e86972d3-e4a0-ad81-45ea-21137e3bfcb6@kylinos.cn>
Date:   Wed, 26 Jan 2022 20:49:18 +0800
From:   Hongyu Xie <xiehongyu1@...inos.cn>
To:     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 Greg,

On 2022/1/26 18:50, Greg KH wrote:
> A: http://en.wikipedia.org/wiki/Top_post
> Q: Were do I find info about this thing called top-posting?
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
>
> A: No.
> Q: Should I include quotations after my reply?
>
> http://daringfireball.net/2007/07/on_top
>
> On Wed, Jan 26, 2022 at 06:22:45PM +0800, 谢泓宇 wrote:
>> 1."What problem?
>> r8152_submit_rx needs to detach netdev if -ENODEV happened, but -ENODEV will
>> never happen
>> because xhci_urb_enqueue only returns -EINVAL if the return value of
>> xhci_check_args <= 0. So
>> r8152_submit_rx will will call napi_schedule to re-submit that urb, and this
>> will cause infinite urb
>> submission.
> Odd line-wrapping...
Sorry about my last reply.
>
> 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.
>
>> 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).

>
> thanks,
>
> greg k-h

thanks,

Hongyu Xie