panics due to buggy ACPI in Dell Latitude E6530?

[kron]

Hi,

I have a Dell notebook (Latitude E6530) on which I track
9-STABLE. It served excellently until mid-Jan when it started
to panic a few times a week or so:

Fatal trap 12: page fault while in kernel mode
cpuid = 3; apic id = 03
fault virtual address	= 0x10116
fault code		= supervisor read data, page not present
instruction pointer	= 0x20:0xffffffff802bc360
stack pointer	        = 0x28:0xffffff848f6db390
frame pointer	        = 0x28:0xffffff848f6db3c0
code segment		= base 0x0, limit 0xfffff, type 0x1b
= DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags	= interrupt enabled, resume, IOPL = 0
current process		= 2199 (conky)
trap number		= 12
panic: page fault
cpuid = 3

Before the panics kernel used to emit messages like:
ACPI Error: No object attached to node 0xfffffe00094a51c0
(20110527/exresnte-138)
ACPI Error: Method execution failed [\_SB_.BAT0._UID] (Node
0xfffffe00094a51c0), AE_AML_NO_OPERAND (20110527/uteval-113)

I suspected it started with a BIOS update (A07 -> A09).
Following the handbook, I took a look at acpidump. Sad to say,
it all was Greek to me, I could't even compile it back using
iasl (35 Errors). However, while skimming it I noticed names
of many versions of Windows and in addition to that, "Linux".
Just to try, I put hw.acpi.osname="Linux" to /boot/loader.conf.
Since that I've never get the panic again (for ~3 weeks).
I hope this is not just a coincidence.

Maybe this experience can help somebody else.

If any of ACPI developers wants to play with the problem
I can provide more info (sorry, no crashdump, was not enabled),
do tests, etc.

BR
Oli