hung process leads to mdb error mdb: failed to read proc at ffffffffb7bb84e0: only 2848 of 3320 byte

I have a hung process and I tried to use pstack to list the stack but it hung.  I tried to do ps -ef from another PuTTY session and it hung.  I tried to do prstat from another PuTTY session and it hung. Three was all the curently open PuTTY sessions that I was willing to hang so I opened a new one and used mdb but it produced an error on one of the ps processes:

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mdb -k
Loading modules: [ unix krtld genunix specfs dtrace uppc pcplusmp cpu.generic cpu_ms.AuthenticAMD.15 ufs md sata fcp fctl qlc sockfs ip hook neti dls sctp arp usba nca zfs lofs cpc random crypto fcip logindmux ptm sppp nfs ipc ]