Re: sysctl -a causes kernel trap 12

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On 1/7/13 5:33 PM, Brandon Gooch wrote:
> On Mon, Jan 7, 2013 at 6:09 PM, Xin Li <delphij_at_delphij.net 
> <mailto:delphij_at_delphij.net>> wrote:
> 
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> On 01/07/13 16:02, Konstantin Belousov wrote:
>> On Mon, Jan 07, 2013 at 03:54:23PM -0800, Xin Li wrote:
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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...
>> 
>> Could you try to isolate the sub-leaf under hw which causes the 
>> panic ? Just shot in the dark, do you have Intel GPU gemified 
>> driver loaded ?
> 
> It seems that it was not hw itself that causes the problem (I
> thought about isolating to sub-leaf and at one point believed it
> was hw.acpi.battery but doing so repeatedly doesn't panic the
> system, with or without INVARIANTS; doing 'sysctl hw' sometimes
> causes panic but not always).
> 
> The laptop is running nVidia but it's using i7-3610QM which does
> have Intel GPU, but I have not loaded drm2.ko and the panic is
> reproducible in single user mode.
> 
> Cheers, - -- Xin LI <delphij_at_delphij.net
> <mailto:delphij_at_delphij.net>> https://www.delphij.net/ FreeBSD -
> The Power to Serve!           Live free or die
> 
> 
> Xin, did you compile the NVIDIA driver port with clang? I was
> having this issue until I set an exception for the NVIDIA driver
> port to be built with GCC.
> 
> Actually, I just remembered (and checked), and what I'm actually
> doing is setting CFLAGS for the NVIDIA driver port to -O0, and
> building with clang. Clang optimizes out important bits, I didn't
> investigate deeply enough to determine what was actually going
> awry...

Yes my nVidia driver is compiled with clang.  I'll try gcc tomorrow,
thanks for the pointer.

(Note that the panic was a NULL pointer deference and it's a race
condition so I doubt if it's compiler related but will try).

Cheers,

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