I see you've got a conversation going with Eric over on zfs-discuss. That's probably your best bet for getting resolution.
I did want to comment on why all the tools point at the nfssys() call as being a problem for nfsd. The way the NFS server is structured, nfsd is used to create service threads, and not much more. The thread dives into the kernel via nfssys(), and that's where it stays. So to find out what the server threads are doing, you need to look in the kernel, below nfssys(). cheers, mike