panic: sleeping thread on r352386

  Hi.

  This panic happens on 1300047 (both r352239 and r352386) with core
i5-7500 as follows. This panic dose not happen on r351728 (1300044).
(The following lines were typed by hand so they might have some miss
typed letters.)

==
Sleeping thread (tid 100177, pid 1814) owns a non-sleepable lock
KDB: stack backtrace of thread 100177:
sched_switch() at sched_switch+0x3f0/frame 0xfffffe008bc0e590
mi_switch() at mi_switch+0x172/frame 0xfffffe008bc0e5c0
sleepq_switch() at sleepq_switch+0x110/frame 0xfffffe008bc0e600
sleepQ-wait() at sleepq_wait+0x43/frame 0xfffffe008bc0e630
vm_page_sleep_if_busy() at (snip)
vm_object_page_remove() at (snip)
vnode_pager_setsize() at (snip)
nfscl_loadattrcache() at (snip)
ncl_writerpc() at (snip)
ncl_doio() at (snip)
nfssvc_iod() at (snip)
fork_exit() at (snip)
fork_trampoline() at (snip)
--- trap 0, rip = 0, rsp = 0, rbp = 0 ---
panic: sleeping thread
cpuid = 3
time = 1568633100
KBD: stack backtrace:
db_trace_self_wrapper() at (snip)
vpanic() at (snip)
(snip)
--- trap 0, rip = 0, rsp = 0, rbp = 0 ---
KDB: enter : panic
[ thread pid 2108 tid 100236 ]
Stopped at     kdb_enter+0x3b: movq   $0,kdb_why
db>
-- 
Masachika ISHIZUKA