sysctl -a causes kernel trap 12

[Xin Li]

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To all: this became more and more hard to replicate lately.  I've
tried these options and the most important progress is that it's
possible to get a crashdump when debug.debugger_on_panic=0 and I
managed to get a backtrace which indicates the panic occur when trying
to do mtx_lock(&Giant) -> __mtx_lock_sleep -> turnstile_wait ->
propagate_priority, but after I've added some instruments to the
surrounding code and enabled INVARIANT and/or WITNESS, it mysteriously
went away.

Reverting my instruments code and update to latest svn makes the issue
disappear for one day.  I've hit it again today but unfortunately
didn't get a successful dump and after reboot I can't reproduce it
again :(

Still trying...

Cheers,
- -- 
Xin LI <delphij at delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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