cannot unmount unreachable nfs server

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http://forums.fedoraforum.org – i restarted my nfs-service usingsystemctl restart nfs-server.servicewhile a client was connected. after the restart the clients mount points were not reachable any more. i was further unable to unmount them usingumount /mnt/point, which led to errors, such as 'stale nfs filehandle'. i tried everything and finally didkillall -9 nfsd nfsiod nfsv4.0-svc nfsd4 nfs4d_callbackandfuser -km /mnt/point, which caused umount to hang forever. i also triedumount -f /mnt/point, but that one hangs, too. does anybody have further ideas? (HowTos)