Re: SG does not ignore dxferp (direct io + mmap)

[Laurence Oberman <loberman@redhat.com>]

----- Original Message -----
> From: "Eyal Ben David" <bdeyal@gmail.com>
> To: "Ewan D. Milne" <emilne@redhat.com>
> Cc: "Johannes Thumshirn" <jthumshirn@suse.de>, dgilbert@interlog.com, "Laurence Oberman" <loberman@redhat.com>,
> linux-scsi@vger.kernel.org
> Sent: Tuesday, November 22, 2016 3:55:44 PM
> Subject: Re: SG does not ignore dxferp (direct io + mmap)
> 
> On Tue, Nov 22, 2016 at 8:30 PM, Ewan D. Milne <emilne@redhat.com> wrote:
> >
> > I see the behavior (zero byte) on the 4.4.34, 4.5.7, 4.6.7, and 4.7.10
> > -stable kernels.  But not (of course) on 4.8.10 -stable.
> >
> > It doesn't look like the sg driver, might be something in the mmap code?
> 
> 
> A kernel guy colleague suggested to look at copy_from_user / copy_to_user
> code.
> It was changed in 4.8
> 
> It was OK with 3.13  (Ubuntu 14.04) but from some kernel (prior or equal to
> 4.4)
> until 4.7 we see the bug. It was somehow fixed at 4.8.
> 
> In order to fully understand what happened, there are two changes to find.
> They might not even be related.
> 
> Thanks!
> Eyal
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> 

So 4.7.9 fails and 4.8.0 works and 4.8.0 is a rebase so we have 

[loberman@localhost linux-stable-4.8.10]$ git log --oneline v4.7.9..v4.8 | wc -l
14552

No obvious single commits stand out for me for copy_from* or copy_to*
There is this:

3fa6c50 mm: optimize copy_page_to/from_iter_iovec
6e05050 sh: fix copy_from_user()
e697100 x86/uaccess: force copy_*_user() to be inlined

I will have to do this the hard way with bisects to figure out which commit addresses this.

Back when I have had enough time to do it.

Thanks
Laurence