sysctl -a causes kernel trap 12

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Hi,

I've recently (by mid-December I think) noticed that sysctl -a can
sometimes cause kernel trap 12.  Tried enabling INVARIANTS and the
problem mysteriously disappeared.  After some experiments on this, it
seems that this can be triggered by sysctl -a but the system have an 1
in 10 chance to survive.  When INVARIANTS is enabled however, I can
not trigger the panic.  "sysctl hw" triggers the panic sometimes, but
not always.

Do anybody have clue on this?  The system hangs hard when it panics so
kernel debugger won't work.  When it panics, the fault instruction
pointer is always 0x20:0xffffffff808d61c9, which is
sys/kern/subr_turnstile.c:297:

> /* Resort td on the list if needed. */ if
> (!turnstile_adjust_thread(ts, td)) { mtx_unlock_spin(&ts->ts_lock);
> // 297 // return; }

This sounds like a race condition but I haven't yet able to track it
down...

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