NFSv4: Add attribute update barriers to delegreturn and pNFS layoutcommit

Ensure that other operations that race with delegreturn and layoutcommit
cannot revert the attribute updates that were made on the server.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Tested-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfs/inode.c

@@ -1555,6 +1555,7 @@ int nfs_post_op_update_inode_force_wcc(struct inode *inode, struct nfs_fattr *fa
 	int status;
 
 	spin_lock(&inode->i_lock);
+	nfs_fattr_set_barrier(fattr);
 	status = nfs_post_op_update_inode_force_wcc_locked(inode, fattr);
 	spin_unlock(&inode->i_lock);
 	return status;