Mentioned 2x in fs/nfs/nfs4state.c but I didn't found the comments.
back ground: fuzzying a 32 bit user mode linux guest brought up (rather rarely, but nevertheless) :
NFS: v4 server returned a bad sequence-id error on an unconfirmed sequence 48f401f0!
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MfG/Sincerely
Toralf Förster
pgp finger print: 7B1A 07F4 EC82 0F90 D4C2 8936 872A E508 7DB6 9DA3