2.5.66 x86_64 oops when swapoff via IA32 emulation

I got this oops from swapoff when shutting down 2.5.66 on
x86_64 with 32-bit user-space (RH8.0). This was from the first
run with 2.5.66, I wasn't able to reproduce it in later runs.

/Mikael

Kernel BUG at page_alloc:687
invalid operand: 0000 [#1]
CPU 0 
Pid: 364, comm: swapoff Not tainted
RIP: 0010:[<ffffffff80143c64>] <ffffffff80143c64>{__free_pages+20}
RSP: 0000:000001000f4a5f30  EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000019 RCX: 0000000000101000
RDX: 0000000000000018 RSI: 0000000000000000 RDI: 0000010001074952
RBP: 000001000fea2bc0 R08: 000000000000fbff R09: 00000000ffffdb68
R10: 000001000f4a4000 R11: 0000000000000000 R12: 0000000000000001
R13: 000001000f62f280 R14: 0000010004360cc0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffffffff802cd5c0(0000) knlGS:00000000a0047080
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000420d40b0 CR3: 0000000000101000 CR4: 00000000000006a0
Process swapoff (pid: 364, stackpage=10001605100)
Stack: ffffffff801531d9 ffffff0000000000 ffffffff802a18a0 0000000000000000 
       ffffffff80155627 000000000804b328 00000000ffffdb68 0000000000000000 
       0000000000000000 0000000000000000 
Call Trace:<ffffffff801531d9>{__vunmap+169} <ffffffff80155627>{sys_swapoff+631} 
       <ffffffff801179fe>{ia32_do_syscall+30} 

Code: 0f 0b ab f3 23 80 ff ff ff ff af 02 ff 4f 08 0f 94 c0 84 c0