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

[Miklos Szeredi <miklos@szeredi.hu>]

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On Sat, Apr 10, 2021 at 7:55 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Sat, Apr 10, 2021 at 8:36 PM Chris Murphy <lists@colorremedies.com> wrote:
> >
> > 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
> >
>
> I'm confused. The error in the title of the page is from overlayfs mount().
> I see no mount in the strace.
> I feel that I am missing some info.
> Can you provide the overlayfs mount arguments
> and more information about the underlying layers?
>
> > 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.
>
> Not sure how fuse-overlayfs is related.
> This is a message from overlayfs kernel driver.
>
> > 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.
> >
>
> OK, so unprivileged overlayfs mount support was added in v5.11
> and it requires opt-in with mount option "userxattr", which could
> explain the problem if tmpfs is used as upper layer.
>
> Do you know if that is the case?
> I sounds to me like it may not be a kernel regression per-se,
> but a regression in the container runtime that started to use
> a new kernel feature?
> Need more context to understand.
>
> Perhaps the solution will be to add user xattr support to tmpfs..

Attached patch.   Tested at some earlier time, since I also bumped
into this issue.

Thanks,
Miklos

[-- Attachment #2: tmpfs-allow-user-xattr.patch --]
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diff --git a/mm/shmem.c b/mm/shmem.c
index d722eb830317..afe59086b3f6 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3250,6 +3250,12 @@ static const struct xattr_handler shmem_trusted_xattr_handler = {
 	.set = shmem_xattr_handler_set,
 };
 
+static const struct xattr_handler shmem_user_xattr_handler = {
+	.prefix = XATTR_USER_PREFIX,
+	.get = shmem_xattr_handler_get,
+	.set = shmem_xattr_handler_set,
+};
+
 static const struct xattr_handler *shmem_xattr_handlers[] = {
 #ifdef CONFIG_TMPFS_POSIX_ACL
 	&posix_acl_access_xattr_handler,
@@ -3257,6 +3263,7 @@ static const struct xattr_handler *shmem_xattr_handlers[] = {
 #endif
 	&shmem_security_xattr_handler,
 	&shmem_trusted_xattr_handler,
+	&shmem_user_xattr_handler,
 	NULL
 };