system stalled, no I/O but 100% CPU from nfs

Cheers,

 This doesn't look good. It goes on for hours. What can be done about it?
(13.4 client & server) 


44 processes:  4 running, 39 sleeping, 1 waiting
CPU:  0.4% user,  0.0% nice, 99.6% system,  0.0% interrupt,  0.0% idle
Mem: 21M Active, 198M Inact, 1190M Wired, 278M Buf, 3356M Free
ARC: 418M Total, 39M MFU, 327M MRU, 128K Anon, 7462K Header, 43M Other
     332M Compressed, 804M Uncompressed, 2.42:1 Ratio
Swap: 15G Total, 15G Free

  PID USERNAME    THR PRI NICE   SIZE    RES STATE    TIME    WCPU COMMAND
  417 root          4  52    0    12M  2148K RUN     20:55  99.12% nfscbd
    0 root         65 -16    -     0B  1040K swapin   0:17   0.64% kernel
11054 root          1  52    0    18M  7664K RUN      0:04   0.10% bsdtar
   11 root         15 -56    -     0B   240K WAIT     0:15   0.05% intr
   16 root          1 -16    -     0B    16K -        0:01   0.03% racctd
11062 root          1  20    0    14M  3804K RUN      0:00   0.03% top
    7 root          3 -16    -     0B    48K psleep   0:00   0.01% pagedaemon
11056 root          1  20    0    21M    10M select   0:00   0.01% sshd
    6 root          1 -16    -     0B    16K -        0:00   0.01% rand_harvest


      Interface           Traffic               Peak                Total
         vtnet0  in      5.380 KB/s          9.113 KB/s          781.439 MB
                 out     4.012 KB/s          8.002 KB/s          674.294 MB


# nfsstat -zc > /dev/null ; sleep 1 ; nfsstat -c
Rpc Counts:
      Getattr      Setattr       Lookup     Readlink         Read        Write       Create       Remove
            1            2            5            0            0            0            0            0
       Rename         Link      Symlink        Mkdir        Rmdir      Readdir     RdirPlus       Access
            0            0            0            0            0            1            0            1
        Mknod       Fsstat       Fsinfo     PathConf       Commit
            0            0            0            0            0
Rpc Info:
     TimedOut      Invalid    X Replies      Retries     Requests
            0            0            0            0           11
Cache Info:
    Attr Hits  Attr Misses    Lkup Hits  Lkup Misses    BioR Hits  BioR Misses    BioW Hits  BioW Misses
           11            1            2            5            0            0            0            0
   BioRL Hits BioRL Misses    BioD Hits  BioD Misses    DirE Hits  DirE Misses    Accs Hits  Accs Misses
            0            0            1            1            1            0            8            1