After upgrade to nfs-utils-2.4.1, my clients were unable to mount nfs v3 exports with the following error in server logs: rpc.mountd: can't stat exported dir /shared/folder: Invalid argument Downgrading to nfs-utils-2.3.3 and everything works as expected. Related bug on https://bugs.gentoo.org/688644 contains proposed patch for support/misc/xstat.c
This is not a kernel problem but a userspace problem. Please report to the nfs-utils maintaner and/or on the linux-nfs@vger.kernel.org.