Re: [PATCH 00/12] ovl: narrow regions protected by directory i_rw_sem

["NeilBrown" <neil@brown.name>]

On Thu, 26 Jun 2025, Amir Goldstein wrote:
> On Wed, Jun 25, 2025 at 1:07 AM NeilBrown <neil@brown.name> wrote:
> >
> > This series of patches for overlayfs is primarily focussed on preparing
> > for some proposed changes to directory locking.  In the new scheme we
> > wil lock individual dentries in a directory rather than the whole
> > directory.
> >
> > ovl currently will sometimes lock a directory on the upper filesystem
> > and do a few different things while holding the lock.  This is
> > incompatible with the new scheme.
> >
> > This series narrows the region of code protected by the directory lock,
> > taking it multiple times when necessary.  This theoretically open up the
> > possibilty of other changes happening on the upper filesytem between the
> > unlock and the lock.  To some extent the patches guard against that by
> > checking the dentries still have the expect parent after retaking the
> > lock.  In general, I think ovl would have trouble if upperfs were being
> > changed independantly, and I don't think the changes here increase the
> > problem in any important way.
> >
> > The first patch in this series doesn't exactly match the above, but it
> > does relate to directory locking and I think it is a sensible
> > simplificaiton.
> >
> > I have tested this with fstests, both generic and unionfs tests.  I
> > wouldn't be surprised if I missed something though, so please review
> > carefully.
> 
> Can you share a git branch for me to pull and test?

My current work tree can be found at
  https://github.com/neilbrown/linux/tree/pdirops
or branch "pdirops" of 
  https://github.com/neilbrown/linux.git

Thanks for the thorough review - I'll work through it and respond over
coming days.

Thanks,
NeilBrown