Reproduceable deadlock in NFS Client

[Peter Jeremy]

My diskless Rock64 has taken to deadlocking reproduceably whilst
building libprivatesqlite3.a as part of buildworld when running
r352792.  At the time of the deadlock, the relevant running process
is:
ar -crD libprivatesqlite3.a sqlite3.o

And those files are:
-rw-r--r--    1 root  wheel  3178496  4 Oct 01:10 libprivatesqlite3.a
-rw-r--r--    1 root  wheel  7975272  4 Oct 01:10 sqlite3.o

The "ar" reports it's in bo_wwait and, after about 30 minutes, I get:
deadlres_td_sleep_q: possible deadlock detected for 0xfffffd00012c9560, blocked for 1800613 ticks

cpuid = 2
time = 1570117920
KDB: stack backtrace:
db_trace_self() at db_trace_self_wrapper+0x28
         pc = 0xffff00000054b83c  lr = 0xffff0000000e2b08
         sp = 0xffff00004030a790  fp = 0xffff00004030a9a0

db_trace_self_wrapper() at vpanic+0x18c
         pc = 0xffff0000000e2b08  lr = 0xffff00000027fb54
         sp = 0xffff00004030a9b0  fp = 0xffff00004030aa50

vpanic() at panic+0x44
         pc = 0xffff00000027fb54  lr = 0xffff00000027f904
         sp = 0xffff00004030aa60  fp = 0xffff00004030aae0

panic() at deadlkres+0x33c
         pc = 0xffff00000027f904  lr = 0xffff00000021c19c
         sp = 0xffff00004030aaf0  fp = 0xffff00004030ab50

deadlkres() at fork_exit+0x7c
         pc = 0xffff00000021c19c  lr = 0xffff0000002404f4
         sp = 0xffff00004030ab60  fp = 0xffff00004030ab90

fork_exit() at fork_trampoline+0x10
         pc = 0xffff0000002404f4  lr = 0xffff00000056743c
         sp = 0xffff00004030aba0  fp = 0x0000000000000000


-- 
Peter Jeremy
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