Re: btrfs+overlayfs: upper fs does not support xattr, falling back to index=off and metacopy=off.

From: Chris Murphy <lists@colorremedies.com>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Chris Murphy <lists@colorremedies.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Btrfs BTRFS <linux-btrfs@vger.kernel.org>,
	overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: btrfs+overlayfs: upper fs does not support xattr, falling back to index=off and metacopy=off.
Date: Sat, 10 Apr 2021 11:36:04 -0600	[thread overview]
Message-ID: <CAJCQCtRGdBzyskifrYLbBGAAm0g7VeC6GeD7xBN-hRqE3GAWYA@mail.gmail.com> (raw)
In-Reply-To: <CAOQ4uxht70nODhNHNwGFMSqDyOKLXOKrY0H6g849os4BQ7cokA@mail.gmail.com>

I can reproduce the bolt testcase problem in a podman container, with
overlay driver, using ext4, xfs, and btrfs. So I think I can drop
linux-btrfs@ from this thread.

Also I can reproduce the title of this thread simply by 'podman system
reset' and see the kernel messages before doing the actual reset. I
have a strace here of what it's doing:

https://drive.google.com/file/d/1L9lEm5n4-d9qemgCq3ijqoBstM-PP1By/view?usp=sharing

It may be something intentional. The failing testcase,
:../tests/test-common.c:1413:test_io_dir_is_empty also has more
instances of this line, but I don't know they are related. So I'll
keep looking into that.

On Sat, Apr 10, 2021 at 2:04 AM Amir Goldstein <amir73il@gmail.com> wrote:

> As the first step, can you try the suggested fix to ovl_dentry_version_inc()
> and/or adding the missing pr_debug() and including those prints in
> your report?

I'll work with bolt upstream and try to further narrow down when it is
and isn't happening.

> > I can reproduce this with 5.12.0-0.rc6.184.fc35.x86_64+debug and at
> > approximately the same time I see one, sometimes more, kernel
> > messages:
> >
> > [ 6295.379283] overlayfs: upper fs does not support xattr, falling
> > back to index=off and metacopy=off.
> >
>
> Can you say why there is no xattr support?

I'm not sure. It could be podman specific or fuse-overlayfs related.
Maybe something is using /tmp in one case and not another for some
reason?

> Is the overlayfs mount executed without privileges to create trusted.* xattrs?
> The answer to that may be the key to understanding the bug.

Yep. I think tmpfs supports xattr but not user xattr? And this example
is rootless podman, so it's all unprivileged.

> My guess is it has to do with changes related to mounting overlayfs
> inside userns, but I couldn't find any immediate suspects.
>
> Do you have any idea since when the regression appeared?
> A bisect would have been helpful here.

Yep. All good ideas. Thanks for the fast reply. I'll report back once
this has been narrowed down futher.

-- 
Chris Murphy