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

[谢泓宇]

Hi Mathias,

On 2022/1/28 17:48, Mathias Nyman wrote:
> Hi
>
> On 28.1.2022 5.48, 谢泓宇 wrote:
> > Hi Mathias,
> >
> > > 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()?
> Yes. That is what it used to return.
> This is more about code maintaining practice than this specific patch.
>
> Only make the necessary change to fix a bug, especially if the patch is going
> to stable kernels.
> The change to return success ("0") instead of -EINVAL in xhci_urb_enqueue() for
> roothub URBs is irrelevant in fixing your issue.
>
> Debugging future issues is a lot harder when there are small undocumented
> unrelated functional changes scattered around bugfixing patches.
>
> Other reason is that even if you can be almost certain xhci_urb_enqueue() won't
> be called for roothub urbs for this kernel version, it's possible some old stable
> kernel code looks very different, and this change can break that stable version.
>
> Seemingly odd checks in code can indicate the old original code was flawed, and
> quickly worked around by adding the odd check.
> That kernel version might still depend on this odd check even if newer versions
> are fixed properly.
>
> > > 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?
> - For all reasons stated above
> - Because it used to, and changing it doesn't fix anything
> - Because urbs sent to xhci_urb_enqueue() should have a valid urb->dev->parent,
>    if they don't have it then they are INVALID
>
> >      2) Should I change all the return statements about xhci_check_args() in drivers/usb/host/xhci.c?
> >
> >      There are 6 of them.
> Only make sure your patch doesn't change the functionality unnecessarily.
> There are two places where we return -EINVAL if xhci_check_args() returns 0:
> xhci_urb_enqueue() and xhci_check_streams_endpoint()
> Keep that functionality.
>
> Thanks
> Mathias

I'll fix these in v2.

Thanks

Hongyu Xie