Re: [PATCH v2 1/2] nfs: fix utimensat() for atime with delegated timestamps

[Jeff Layton]

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@xxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>