2.6.28: Oops at acpi_ds_exec_end_op+0x1b: kills machine

[Mark Lord <lkml@rtr.ca>]

This happened on our Mythtv box at startup this morning:
The Oops happened once only, at system startup, on initial device probe.
Not reproduceable, so probably a rare race of some kind.
The xc5000 module was loaded with "init_fw=1" to force f/w load on modprobe.

2.6.28 kernel, SMP, x86_64, two CPUs (Core2duo 1.86GHz), 2GB RAM.

Oops text typed in by hand from screen photos
( original photos: http://rtr.ca/xc5000_lockup )
...
xc5000: firmware read 12332 bytes.
xc5000: firmware upload
BUG kernel NULL pointer dereference at 000000000000000c
IP: [<ffffffff8038fbcf>] acpi_ds_exec_end_op+0x1b/0x3c4
PGD 7c8cd067 PUD 7d411067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
last sysfs file: /sys/class/firmware/i2c-2/loading
CPU 0
...
Modules linked in: xc5000 au8522 tea5767 tda9887 tda8290 tea5761 fuse au0828(+)
dvd_core usbhid tuner_simple tuner_types snd_hda_intel msp3400 ... nvidia(P) ...
...
Pid: 2383, comm: modprobe Tainted: P A 2.6.28 #9  
RIP: 0010:[<ffffffff8038fbcf>]  [<ffffffff8038fbcf>] acpi_ds_exec_end_op+0x1b/0x3c4
RSP: 0018:ffff88007a095ad8  EFLAGS: 00010296
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88007f8588f0
R10: ffff88007f8a4d40 R11: ffff8800000bf9e0 R12: 0000000000000000
R13: ffff88007e43bc10 R14: ffff88007a0ac000 R15: ffff88007e43bc10
FS:  00007f844d5666e0(0000) GS:ffffffff8060f540(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
...
Process modprobe (pid: 2383, threadinfo ffff88007a094000, task ffff88007fa043d0)
Stack:
 ffff88007a085380 0000000000000000 ffff88007a085380 ffffffffa09cfb28
 ffff88007e43bc10 ffffffffa09f263f ffff88007a095b18 ffff88007a085380
 ffffc200109e6000 ffff88007a085380 000000000000f9f9 00000000000094d7
Call Trace:
xc_load_fw_and_init_tuner+0x14b/0x29c [xc5000]
i2c_transfer+0x8a/0x94
xc5000_init+0x3d/0x6f [xc5000]
xc5000_attach+0x22c/0x256 [xc5000]
__symbol_get+0x2c/0xd3
au0828+dvb_register+0x2ec/x5cb [au0828]
au0828_usb_probe+0x10c/0x140 [au0828]
usb_match_id+0x32/0x58 [usbcore]
usb_probe_interface+0xfb/0x132 [usbcore]
driver_probe_device+0xb5/0x159
__driver_attach+0x59/0x80
__driver_attach+0x0/0x80
bus_for_each_dev+0x44/0x78
bus_add_driver+0xac/0x1f2
driver_register+0xa2/0x11f
usb_register_driver+0x7e/0xe0 [usbcore]
au0828_init+0x0/0xbb [au0828]
au0828_init+0xa1/0xbb [au0828]
_stext+0x56/0x14f
vma_link+0x90/0xa2
update_curr+0x49/0xf0
enqueue_task_fair+0x14c/0x161
check_preempt_wakeup+0xf4/0x124
try_to_wake_up+0x16a/0x17c
sys_init_module+0xa0/0x1a9
system_call_fastpath+0x16/0x1b
Code: 00 66 c7 40 0c c0 00 89 d8 48 83 c4 18 5b 5d c3 41 55 41 54 55 48 89
 48 83 ec 08 48 8b 87 08 03 00 00 4c 8b a7 00 03 00 00 <8a> 50 0c 8a 40 0?
 c8 83 f9 0a 75 25 41 0f b7 4c 24 0a 48
RIP  [<ffffffff8038fbcf>] acpi_ds_exec_end_op+0x1b/0x3c4
 RSP <ffff88007a095ad8>
CR2: 000000000000000c
---[ end trace c23df576c022eb7e ]---

Could someone perhaps explain how acpi_ds_exec_end_op even enters the
picture here?  I'm confused by that.

The driver was doing/completing an i2c firmware transfer at the time of
the oops.

Thanks