NACK: [SRU][UNSTABLE/FOCAL/BIONIC][PATCH v2] UBUNTU: SAUCE: shiftfs: fix dentry revalidation

[Christian Brauner]

On Tue, May 19, 2020 at 07:43:21AM +0200, Stefan Bader wrote:
> On 18.05.20 20:18, Christian Brauner wrote:
> > BugLink: https://bugs.launchpad.net/bugs/1879196
> > 
> > While fixing [1] we introduced a regression and triggered [2] whereby
> > the underlay and overlay go out of sync because they disagree about the
> > dcache. Such situation easily arise when the underlay is modified
> > directly. This means the overlay needs to revalidate the dentry in the
> > dcache to catchup with the underlay.
> > 
> > Note, in general it's not advisable to directly modify the underlay
> > while a shiftfs mount is on top. In some way this means we need to keep
> > two caches in sync and it's hard enough to keep a single cache happy.
> > But shiftfs' use-case is inherently prone to be used for exactly that.
> > So this is something we have to navigate carefully and honestly we have
> > no full model upstream that does the same. Overlayfs has the copy-up
> > behavior which let's it get around most of the issues but we don't have
> > it and ecryptfs is broken in such scenarios which we verified quite a
> > while back.
> > In any case, I built a kernel with this patch and re-ran all regressions
> > that are related to this that we have so far (cf.  [1], [2], and [3]).
> > None of them were reproducible with this patch here. So we still fix the
> > ESTALE issue but also keep underlay and overlay in sync.
> 
> This test kernel should be provided to the bug reporter, so it can be confirmed
> to fix the issue there as well.

See
https://drive.google.com/open?id=19iTwaFSYNS95_I-gD_rvFoV9cMAfy6io
Elmo is also Cced here. I don't have any other place I can upload this,
I think.

> But more importantly, you submitted this for Bionic and there is no shiftfs in
> that release. Only Eoan. I am not convinced you tried at least to apply the

Yeah, sorry that's always my thing mixing up that shiftfs is in Eoan and
not in Bionic.
Similar to all the other patches, Eoan doesn't need a separate patch
I've verified this on top of Eoan master-next that has all the other
shiftfs patches:

ubuntu at amdgpu:~/linux/ubuntu/ubuntu-eoan$ git am ./0001-UBUNTU-SAUCE-shiftfs-fix-dentry-revalidation.patch
Applying: UBUNTU: SAUCE: shiftfs: fix dentry revalidation

on top of

ubuntu at amdgpu:~/linux/ubuntu/ubuntu-eoan$ git am ./0001-UBUNTU-SAUCE-shiftfs-fix-dentry-revalidation.patch
Applying: UBUNTU: SAUCE: shiftfs: fix dentry revalidation
commit d53d4b6679bb89ae78787dca0fea951752e27d48 (upstream/master-next)
Author: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
Date:   Fri May 15 13:03:42 2020 +0200

    UBUNTU: Ubuntu-5.3.0-54.48

    Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

I'm not letting shiftfs across kernel versions go out of sync precisely
(at least until we absolutely have to) so that patches can be applied
trivially across releases so it's easier for all of you.

Thanks!
Christian