spin lock sched lock held by 0xffffff007b7d2940 for > 5 seconds

Found a panic on my bos this morning:
spin lock sched lock held by 0xffffff007b7d2940 for > 5 seconds
panic: spin lock held too long
cpuid = 1
KDB: stack backtrace:
kdb_backtrace() at kdb_backtrace+0x37
panic() at panic+0x1d1
_mtx_lock_spin() at _mtx_lock_spin+0xd0
_mtx_lock_spin_flags() at _mtx_lock_spin_flags+0xcc
hardclock_process() at hardclock_process+0x47
forwarded_hardclock() at forwarded_hardclock+0x21
Xhardclock() at Xhardclock+0x76
tc_windup() at tc_windup+0x113
tc_setclock() at tc_setclock+0xc7
settime() at settime+0x160
clock_settime() at clock_settime+0x87
syscall() at syscall+0x320
Xfast_syscall() at Xfast_syscall+0xa8
--- syscall (233, FreeBSD ELF64, clock_settime), rip = 0x2007b53ec, rsp 
= 0x7fff
ffffeb38, rbp = 0x7fffffffeb80 ---
KDB: enter: panic

BUT KDB does not let me in....

So cant offer anything other than this.

--WjW