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SubjectRe: [PATCH 4.19 114/149] UAS: Revert commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments")
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
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
no-regressions policy, we only need to revert the commit -- which you
have already done.

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.

Alan Stern

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