Panic in ld_ldt() @r292914 (amd64) -- just after launching CPUs

[David Wolfskill]

Found this on both my build machine and my laptop, each of which just
built head @r292914 (while running r292864 during the build) -- e.g.:

FreeBSD g1-252.catwhisker.org 11.0-CURRENT FreeBSD 11.0-CURRENT #287  r292864M/292864:1100092: Tue Dec 29 05:01:42 PST 2015     root at g1-252.catwhisker.org:/common/S4/obj/usr/src/sys/CANARY  amd64

Unfortunately, the panic occurs early enough that I can't get a crash
dump (I'm don't think the swap device has yet been discovered), and
serial console isn't working for my build machine.

I took some screen shots of the laptop, but I don't seem to be able
to connect the phone to the laptop in a way to allow data interchange,
so I'll try to hand-transcribe the more obviously-relevant bits:

...
SMP: AP CPU #5 Launched!
kernel trap 9 with interrupts disabled

Fatal trap 9: general protection fault while in kernel mode
cpuid = 6; apic id = 86
instruction pointer	= 0x28:0xffffffff80d9b505
stack pointer		= 0x28:0xfffffe06015ca8f0
frame pointer		= 0x28:0xfffffe06015ca950
code segment		= base 0x0, limit 0xfffff, type 0x1b
			= DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags	= resume, IOPL = 0
current process		= 11 (idle: cpu6)
[ thread pid 11 tid 100010 ]
Stopped at	0xffffffff80d9b505 = ld_ldt:	lldt	%ax
db> bt
Tracing pid 11 tid 100010 td 0xfffff800067f69a0
ld_ldt() at 0xffffffff80d9b505 = ld_ldt/frame 0xfffffe06015ca900
sched_switch() at 0xffffffff80a176c5 = sched_switch+0x495/frame 0xfffffe06015ca950
mi_switch() at 0xffffffff809f8759 = mi_switch+0x169/frame 0xfffffe06015ca980
sched_idletd() at 0xffffffff80a1a211 = sched_idletd+0x391/frame 0xfffffe06015caa70
fork_exit() at 0xffffffff809b5324 = fork_exit+0x84/frame 0xfffffe06015aab0
fork_trampoline() at 0xffffffff80d9eade = fork_trampoline+0xe/frame 0xfffffe06015caab0
--- trap 0, rip = 0, rsp = 0, rpb = 0 ---
db> 

I'm happy to try testing, but as I actually use the laptop for
day-to-day activities, I'm likely to need to do some priority-shifting.

Peace,
david
-- 
David H. Wolfskill				david at catwhisker.org
Those who would murder in the name of God or prophet are blasphemous cowards.

See http://www.catwhisker.org/~david/publickey.gpg for my public key.
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