On Sun, 10 Nov 2019, Oliver Neukum wrote:
> Am Freitag, den 08.11.2019, 10:35 -0500 schrieb Alan Stern:
> > On Fri, 8 Nov 2019, Greg Kroah-Hartman wrote:
> >
> > > On Thu, Nov 07, 2019 at 12:32:45PM +0100, Oliver Neukum wrote:
> > > > Am Dienstag, den 05.11.2019, 17:38 +0100 schrieb Greg Kroah-Hartman:
> > > > > > > Given this information, perhaps you will decide that the revert is
> > > > > > > worthwhile.
> > > > > >
> > > > > > Damned if I do, damned if I do not.
> > > > > > Check for usbip and special case it?
> > > > >
> > > > > We should be able to do that in the host controller driver for usbip,
> > > > > right? What is the symptom if you use a UAS device with usbip and this
> > > > > commit?
> > > >
> > > > Yes, that patch should then also be applied. Then it will work.
> > > > Without it, commands will fail, as transfers will end prematurely.
> > >
> > > Ok, I'm confused now. I just checked, and I really have no idea what
> > > needs to be backported anymore. 3ae62a42090f ("UAS: fix alignment of
> > > scatter/gather segments") was backported to all of the stable kernels,
> > > and now we reverted it.
> > >
> > > So what else needs to be done here?
> >
> > In one sense, nothing needs to be done. 3ae62a42090f was intended to
> > fix a long-standing problem with USBIP, but people reported a
>
> OK, now I am a bit confused. AFAICT 3ae62a42090f actually did fix the
> issue. So if you simply revert it, the issue will reappear.
Correct. I think.
> > regression in performance. (Admittedly, the report was about the
> > correponding change to usb-storage, not the change to uas, but it's
> > reasonable to think the effect would be the same.) So in line with the
>
> Yes.
>
> > no-regressions policy, we only need to revert the commit -- which you
> > have already done.
>
> But that breaks UAS over USBIP, doesn't it?
It was already broken to start with. The attempted fix caused a
regression, so the fix must be reverted.
> > On the other hand, the long-standing problem in USBIP can be fixed by
> > back-porting commit ea44d190764b. But since that commit isn't a
> > bug-fix (and since it's rather large), you may question whether it is
> > appropriate for the -stable kernel series.
>
> It certainly is large. But without it UAS won't work over USBIP, will
> it? I think that is the central question we need to answer here.
You are right. If Greg is okay with porting ea44d190764b to the stable
kernels, I won't object.
Alan Stern
