During boot of i386 2.6.24 kernels with CONFIG_BLK_DEV_CMD640 set on 
VirtualBox 1.5.2, I get the following failure:

<snip>
@@: buggy cmd640<3>BUG soft lockup - CPU#0 stuck for 11s! [modprobe:572]

Pid: 572, comm: modprobe Not tainted (2.6.24-rc2 #1)
EIP: 0060:[<c02a3546>] EFLAGS: 00000286 CPU: 0
EIP is at _spin_lock_irqsave+0x11/0x27
EAX: d0be66b4 EBX: d0bb0b74 ECX: c039a760 EDX: 00000246
ESI: 00000000 EDI: 00000052 EBP: d0be6840 ESP: cec13df0
 DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0069
CR0: 8005003b CR2: ffffffff CR3: 0ec3b000 CR4: 000006d0
DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
DR6: 00000000 DR7: 00000000
 [<d0bd7ef2>} put_cmd640_reg+0x11/0x30 [ide_core]
 [<d081aa00>] ide_probe_for_cmd640x+0x2bd/0x450 [ide_core]
 [<c01980e4>] create_proc_entry+0x72/0x86
 [<d081a6a0>] init_module+0x577/0x586 [ide_core]
 [<c011d46b>] default_wake_function+0x0/0x8
 [<c014120b>] sys_init_module+0x1672/0x172a
 [<c01d0f44>] rb_insert_color+0x4c/0xd
 [<c014c540>] disable_irq+0x0/0x25
 [<c0103e36>] syscall_call+0x7/0xb
 ==================
</snip>

After some time the "BUG soft lockup" repeats.

The first 2 characters on the first line (where I put "@@") look to be 
unicode characters 2630 and 2665 (hex). The code that prints the message is 
in drivers/ide/pci/cmd640.c (762):
     printk("%s: buggy cmd640%c interface on %s, config=0x%02x\n",
            cmd_hwif0->name, 'a' + cmd640_chip_version - 1, bus_type, cfr);

Note that the message is not printed completely.

The BUG does not occur if I boot with 2.6.22 or 2.6.23 and disappears if I 
compile 2.6.24 with CONFIG_BLK_DEV_CMD640 unset.

VirtualBox does not have CMD64x, but ATA_PIIX.

Cheers,
FJP