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SubjectRe: [PATCH v2 1/2] nfs: fix utimensat() for atime with delegated timestamps
Hi Jeff and all,

With this patch and running against a server that would update the
c/mtime of a GETATTR in a compound with CLONE(COPY), the timestamps
is (might be) going "backwards"? I see that SETATTR+DELEGRETURN (after
the CLONE) is setting a timestamp which is earlier than what's
returned by the server in the GETATTR. Though I haven't figured out
how to "show" it via test (I observe it on a network trace).

This is seen testing either against Hammerspace which already updates
the values or the linux server with the patch I'm working on to update
timestamp for CLONE/COPY.

I have to say I haven't figured out if this patch needs to modify such
that it fixes 221 but doesn't break 407 or we are fundamentally
dealing with a problem of including a GETATTR in a compound while
holding an attribute delegation that needs to be solved differently.
Like I said before, if the server were to update the value upon
receiving the GETATTR in the compound (regardless of the origin),
should it then do a CB_GETATTR first (which I already grumbled seems
like a poor choice)? Or, should the client be changed to not send a
GETATTR in CLONE of the compounds if it's holding an attribute
delegation and somehow figure out attributes differently then it does
now.


On Wed, Mar 25, 2026 at 8:30 AM Jeff Layton <jlayton@kernel.org> wrote:
>
> On Tue, 2026-03-24 at 13:32 -0400, Jeff Layton wrote:
> > xfstest generic/221 is failing with delegated timestamps enabled. When
> > the client holds a WRITE_ATTRS_DELEG delegation, and a userland process
> > does a utimensat() for only the atime, the ctime is not properly
> > updated. The problem is that the client tries to cache the atime update,
> > but there is no mtime update, so the delegated attribute update never
> > updates the ctime.
> >
> > Delegated timestamps don't have a mechanism to update the ctime in
> > accordance with atime-only changes due to utimensat() and the like.
> > Change the client to issue an RPC in this case, so that the ctime gets
> > properly updated alongside the atime.
> >
> > Fixes: 40f45ab3814f ("NFS: Further fixes to attribute delegation a/mtime changes")
> > Reported-by: Olga Kornievskaia <aglo@umich.edu>
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > fs/nfs/inode.c | 9 +--------
> > 1 file changed, 1 insertion(+), 8 deletions(-)
> >
> > diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
> > index 4786343eeee0f874aa1f31ace2f35fdcb83fc7a6..3a5bba7e3c92d4d4fcd65234cd2f10e56f78dee0 100644
> > --- a/fs/nfs/inode.c
> > +++ b/fs/nfs/inode.c
> > @@ -757,14 +757,7 @@ nfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> > } else if (nfs_have_delegated_atime(inode) &&
> > attr->ia_valid & ATTR_ATIME &&
> > !(attr->ia_valid & ATTR_MTIME)) {
> > - if (attr->ia_valid & ATTR_ATIME_SET) {
> > - if (uid_eq(task_uid, owner_uid)) {
> > - spin_lock(&inode->i_lock);
> > - nfs_set_timestamps_to_ts(inode, attr);
> > - spin_unlock(&inode->i_lock);
> > - attr->ia_valid &= ~(ATTR_ATIME|ATTR_ATIME_SET);
> > - }
> > - } else {
>
> This probably deserves a comment. How about something like:
>
> /*
> * An atime-only update via an explicit setattr (e.g.: utimensat() and
> * the like) requires updating the ctime as well. Delegated timestamps
> * don't have a mechanism for updating the ctime with a delegated
> * atime-only update, so an RPC must be issued.
> */
>
> > + if (!(attr->ia_valid & ATTR_ATIME_SET)) {
> > nfs_update_delegated_atime(inode);
> > attr->ia_valid &= ~ATTR_ATIME;
> > }
>
> --
> Jeff Layton <jlayton@kernel.org>

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