[PATCH 2/2] nfsd: Honor delegated timestamps when change and size match

[Jeff Layton]

nfsd4_deleg_getattr_conflict() applies time_deleg_access and
time_deleg_modify from a CB_GETATTR reply only when the reply's change
attribute or size differs from the server's. RFC 9754 section 5 makes
the holder of a timestamp delegation the authority for atime and mtime,
and puts no such condition on accepting them.

Because the delegation's file has FMODE_NOCMTIME, the holder's WRITEs
change neither mtime nor the change attribute on the server. After a
flushed WRITE, the CB_GETATTR reply matches on change and size, the
holder's mtime is dropped, and other clients see new data with the
pre-WRITE mtime. Since commit 304d81a2fbf2 ("nfsd: fix file change
detection in CB_GETATTR") compares against the current file size, this
also hits flushed extending WRITEs. Holder reads lose the atime the
same way.

- For timestamp delegations, always vet and apply the CB_GETATTR
  times.
- If that advances mtime, mark the file modified so that GETATTR
  reports a new change attribute (RFC 9754: the change time is derived
  from the modify time). An atime-only update must not advance the
  change time, so leave the file unmodified in that case.

Fixes: 6ae30d6eb26b ("nfsd: add support for delegated timestamps")
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 fs/nfsd/nfs4state.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index cd70d86f4bc6..418b3ee37c68 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -10751,6 +10751,13 @@ static int cb_getattr_update_times(struct dentry *dentry, struct nfs4_delegation
 	inode_lock(inode);
 	ret = notify_change(&nop_mnt_idmap, dentry, &attrs, NULL);
 	inode_unlock(inode);
+
+	/*
+	 * FMODE_NOCMTIME kept the holder's WRITEs from bumping the change
+	 * attribute; a newer delegated mtime is the only evidence of them.
+	 */
+	if (!ret && (attrs.ia_valid & ATTR_MTIME))
+		ncf->ncf_file_modified = true;
 	return ret;
 }
 
@@ -10836,7 +10843,11 @@ nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct dentry *dentry,
 		else if (i_size_read(inode) != ncf->ncf_cb_fsize)
 			ncf->ncf_file_modified = true;
 	}
-	if (ncf->ncf_file_modified) {
+	/*
+	 * The holder of a timestamp delegation is the authority for atime
+	 * and mtime (RFC 9754, section 5), even if change and size match.
+	 */
+	if (ncf->ncf_file_modified || deleg_attrs_deleg(dp->dl_type)) {
 		int err;
 
 		/*
@@ -10849,6 +10860,8 @@ nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct dentry *dentry,
 			status = nfserrno(err);
 			goto out_status;
 		}
+	}
+	if (ncf->ncf_file_modified) {
 		ncf->ncf_cur_fsize = ncf->ncf_cb_fsize;
 		*pdp = dp;
 		return nfs_ok;

-- 
2.56.0