[Samba] Win7 clients problem after upgrading samba file server to 4.12 on Arch

[Jeremy Allison]

On Sat, May 09, 2020 at 03:32:05PM +0200, Ralph Boehme via samba wrote:
> Am 5/9/20 um 3:11 PM schrieb pavlos:
> > sob., 9 maj 2020 o 14:37 Ralph Boehme <slow at samba.org
> > <mailto:slow at samba.org>> napisał(a):
> > 
> >     To be clear: if you're running into this issue that I'm seeing in the
> >     code, then this is *not* a client side bug. It's a server bug that only
> >     gets triggered by a specific access pattern. Likely Win 7 has a
> >     different pattern compared to other Windows versions which explains why
> >     you only see it there.
> > 
> >     -slow
> > 
> > 
> > Ralf,
> > Give me a while, I have to prepare the server moving it to the commit we
> > have our focus on.
> 
> I guess we can avoid that, the issue should be present in any version
> after that commit.
> 
> >   * Windows Explorer - this tool could display a folder content, go into
> >     a subfolder, but any attempt to skip back two folders up in the
> >     address bar always was producing this funny message "/The process
> >     cannot access the file because it is being used by another process./" 
> 
> this sounds like a reliable and simple reproducer, so please use this
> access pattern when trying to reproduce the issue.
> 
> Fwiw, I've written a testcase that excercises the supposed problematic
> access pattern and can reproduce a server bug in the commit you've bisected.
> 
> I have a WIP fix for master, can you give it a whirl?
> 
> CI: https://gitlab.com/samba-team/devel/samba/pipelines/144360879

Actually, now I've looked at the test case reproducer I don't
feel at all bad that Volker didn't spot it in the original code,
or that I didn't spot it in my review :-).

That's such a pathalogical case that without the reproducer
showing how it happens I don't think we'd *ever* have spotted
this regression :-).

That's why user help is *so* important ! Thanks so much for
helping track down this regression.