It appears that 

commit 6c99e9ad47d9c082bd096f42fb49e397b05d58a8
Author: Rusty Russell <rusty@rustcorp.com.au>
Date:   Tue Nov 25 02:35:04 2008 +1030

    sched: convert struct sched_group/sched_domain cpumask_ts to variable bitmaps

    Impact: (future) size reduction for large NR_CPUS.

    We move the 'cpumask' member of sched_group to the end, so when we
    kmalloc it we can do a minimal allocation: saves space for small
    nr_cpu_ids but big CONFIG_NR_CPUS.  Similar trick for 'span' in
    sched_domain.

    This isn't quite as good as converting to a cpumask_var_t, as some
    sched_groups are actually static, but it's safer: we don't have to
    figure out where to call alloc_cpumask_var/free_cpumask_var.

    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


causes a panic in ia64 with NR_CPUS=1024.  Config attached though I think
it's the standard config file in:

	//git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6

Version: v2.6.28-5274-g597b0d2

Revert it and the problem goes away.

Thanks!
Mike


Calibrating delay loop... 3325.95 BogoMIPS (lpj=6651904)
Brought up 128 CPUs
Total of 128 processors activated (412352.51 BogoMIPS).
Unable to handle kernel paging request at virtual address 0001000000000007
swapper[1]: Oops 8804682956800 [1]
Modules linked in:

Pid: 1, CPU 0, comm:              swapper
psr : 00001010085a6018 ifs : 8000000000000691 ip  : [<a0000001000959a0>]    Not tainted (2.6.28)
ip is at cpu_attach_domain+0x1a0/0x800
unat: 0000000000000000 pfs : 0000000000000691 rsc : 0000000000000003
rnat: 0000000000000000 bsps: 0000000000000000 pr  : 0000000000005941
ldrs: 0000000000000000 ccv : 0000000000000000 fpsr: 0009804c8a70433f
csd : 0000000000000000 ssd : 0000000000000000
b0  : a000000100095890 b6  : a00000010008f180 b7  : a00000010008f180
f6  : 0fff2fffffffff0000000 f7  : 0fffb8000080000000000
f8  : 1001f800007ff80000000 f9  : 1000b8000000000000000
f10 : 10013800007ff77ffff80 f11 : 1003e0000000000100000
r1  : a000000101192740 r2  : 000000000000028f r3  : 0000000000000400
r8  : 0000000000000001 r9  : 0000000000000000 r10 : 0000000000000000
r11 : 0000000000000000 r12 : e0001160f0d4f820 r13 : e0001160f0d40000
r14 : 0000000000000001 r15 : 0000000000000000 r16 : 0000000000000001
r17 : 0001000000000007 r18 : 0000000000000010 r19 : a000000100eb5028
r20 : a000000101004010 r21 : a000000101004010 r22 : 0000000000000080
r23 : 0000000000000080 r24 : a000000100df4658 r25 : 0000ffffffffffff
r26 : a000000101004010 r27 : a000000101004010 r28 : a000000101004010
r29 : 0000000000000080 r30 : a000000100db0080 r31 : a000000100f92c80

Call Trace:
 [<a000000100015e20>] show_stack+0x40/0xa0
                                sp=e0001160f0d4f3f0 bsp=e0001160f0d41008
 [<a000000100016730>] show_regs+0x850/0x8a0
                                sp=e0001160f0d4f5c0 bsp=e0001160f0d40fa8
 [<a000000100039cd0>] die+0x1b0/0x2c0
                                sp=e0001160f0d4f5c0 bsp=e0001160f0d40f60
 [<a00000010005dc30>] ia64_do_page_fault+0x8d0/0xa40
                                sp=e0001160f0d4f5c0 bsp=e0001160f0d40f10
 [<a00000010000c340>] ia64_native_leave_kernel+0x0/0x270
                                sp=e0001160f0d4f650 bsp=e0001160f0d40f10
 [<a0000001000959a0>] cpu_attach_domain+0x1a0/0x800
                                sp=e0001160f0d4f820 bsp=e0001160f0d40e88
 [<a00000010009e400>] __build_sched_domains+0xe20/0xfe0
                                sp=e0001160f0d4f9a0 bsp=e0001160f0d40df0
 [<a000000100b7c8c0>] sched_init_smp+0x1a0/0x640
                                sp=e0001160f0d4fdb0 bsp=e0001160f0d40dc8
 [<a000000100b60680>] kernel_init+0x460/0x5a0
                                sp=e0001160f0d4fe30 bsp=e0001160f0d40da8
 [<a000000100014370>] kernel_thread_helper+0xd0/0x100
                                sp=e0001160f0d4fe30 bsp=e0001160f0d40d80
 [<a00000010000a4c0>] start_kernel_thread+0x20/0x40
                                sp=e0001160f0d4fe30 bsp=e0001160f0d40d80
Kernel panic - not syncing: Attempted to kill init!