irq 7: nobody cared (try booting with the "irqpoll" option)

Binary package hint: linux-headers-2.6.15-27-686

OS: Ubuntu 6.06.1 LTS
Hardware: Shuttle SB75G2 motherboard (Intel 875 based)
Audio Hardware: Intel ICH5 - snd_intel8x0

Some time after booting up, my sound stops working. I see the following message in the kernel log:

Sep 22 10:33:50 localhost kernel: [17214565.236000] irq 7: nobody cared (try booting with the "irqpoll" option)
Sep 22 10:33:50 localhost kernel: [17214565.236000] [__report_bad_irq+42/160] __report_bad_irq+0x2a/0xa0
Sep 22 10:33:50 localhost kernel: [17214565.236000] [handle_IRQ_event+61/112] handle_IRQ_event+0x3d/0x70
Sep 22 10:33:50 localhost kernel: [17214565.236000] [note_interrupt+135/240] note_interrupt+0x87/0xf0
Sep 22 10:33:50 localhost kernel: [17214565.236000] [__do_IRQ+253/272] __do_IRQ+0xfd/0x110
Sep 22 10:33:50 localhost kernel: [17214565.236000] [do_IRQ+25/48] do_IRQ+0x19/0x30
Sep 22 10:33:50 localhost kernel: [17214565.236000] [common_interrupt+26/32] common_interrupt+0x1a/0x20
Sep 22 10:33:50 localhost kernel: [17214565.236000] [mwait_idle+42/64] mwait_idle+0x2a/0x40
Sep 22 10:33:50 localhost kernel: [17214565.236000] [cpu_idle+111/192] cpu_idle+0x6f/0xc0
Sep 22 10:33:50 localhost kernel: [17214565.236000] [start_kernel+415/512] start_kernel+0x19f/0x200
Sep 22 10:33:50 localhost kernel: [17214565.236000] [unknown_bootoption+0/496] unknown_bootoption+0x0/0x1f0
Sep 22 10:33:50 localhost kernel: [17214565.236000] handlers:
Sep 22 10:33:50 localhost kernel: [17214565.236000] [pg0+543238400/1069167616] (snd_intel8x0_interrupt+0x0/0x2a0 [snd_intel8x0])
Sep 22 10:33:50 localhost kernel: [17214565.236000] Disabling IRQ #7

I tried booting with the "irqpoll" option, but that causes other strange behavior (The drive appears confused (ireason = 0x01)).

I then booted with these options: "acpi=debug pci=routeirq apic=debug". dmesg shows:

Bad page state at free_hot_cold_page (in process 'aplay', page c13cff24)
flags:0x80000414 mapping:00000000 mapcount:0 count:0
Backtrace:
 [<c0155027>] bad_page+0x87/0xc0
 [<c01559bc>] free_hot_cold_page+0x4c/0x140
 [<c0161a88>] zap_pte_range+0x258/0x310
 [<c0161c36>] unmap_page_range+0xf6/0x130
 [<c0161d40>] unmap_vmas+0xd0/0x250
 [<c0166a52>] unmap_region+0xb2/0x160
 [<c0166df9>] do_munmap+0x109/0x150
 [<c0166e91>] sys_munmap+0x51/0x80
 [<c0103417>] sysenter_past_esp+0x54/0x75
Trying to fix it up, but a reboot is needed

During a search, I found a message referencing a patch (http://lkml.org/lkml/2005/11/20/28). I installed the linux-source-2.6.15 package. I tried apply the patch from the email, but it appears that these sources already have that patch:

root@foo:/usr/src# patch --dry-run -p0 -i patches-2.6.15/audio-mem.patch
missing header for unified diff at line 3 of patch
patching file linux/sound/core/memalloc.c
Reversed (or previously applied) patch detected! Assume -R? [n]
Apply anyway? [n]
Skipping patch.
2 out of 2 hunks ignored -- saving rejects to file linux/sound/core/memalloc.c.rej

I'm not sure if this matters, or if I'm looking in the right place, but /proc/interrupts seems to say that irq7 is not being shared:

root@foo:/usr/src# cat /proc/interrupts | grep 7
  7: 5355 XT-PIC Intel ICH5

Any help would be appreciated.

Thanks,

--Alex