Re: Panic in ld_ldt() _at_r292914 (amd64) -- just after launching CPUs

On Wed, Dec 30, 2015 at 05:54:07AM -0800, David Wolfskill wrote:
> Found this on both my build machine and my laptop, each of which just
> built head _at_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.
> 

Try clean build first.  struct proc layout was changed recently, and the
instruction at ld_ldt would fault if using the wrong offsets.