Re: [bisected] 2.6.31 regression: fails to boot as xen guest

[Pekka Enberg]

Hi Arnd,

On Tue, Aug 25, 2009 at 6:48 PM, Arnd
Hannemann<hannemann@xxxxxxxxxxxxxxxxxxx> wrote:
> current 2.6.31 fails to boot on our xen host (32bit pae).
> Unfortunately it fails in a way that there is absolutely no output
> on the console. Config is as 32bit guest.
>
> Git bisect gave the following:
>
> 83b519e8b9572c319c8e0c615ee5dd7272856090 is first bad commit
> commit 83b519e8b9572c319c8e0c615ee5dd7272856090
> Author: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
> Date:   Wed Jun 10 19:40:04 2009 +0300
>
>    slab: setup allocators earlier in the boot sequence
>
>    This patch makes kmalloc() available earlier in the boot sequence so we can get
>    rid of some bootmem allocations. The bulk of the changes are due to
>    kmem_cache_init() being called with interrupts disabled which requires some
>    changes to allocator boostrap code.
>
>    Note: 32-bit x86 does WP protect test in mem_init() so we must setup traps
>    before we call mem_init() during boot as reported by Ingo Molnar:
>
>      We have a hard crash in the WP-protect code:
>
>      [    0.000000] Checking if this processor honours the WP bit even in supervisor mode...BUG: Int 14: CR2 ffcff000
>      [    0.000000]      EDI 00000188  ESI 00000ac7  EBP c17eaf9c  ESP c17eaf8c
>      [    0.000000]      EBX 000014e0  EDX 0000000e  ECX 01856067  EAX 00000001
>      [    0.000000]      err 00000003  EIP c10135b1   CS 00000060  flg 00010002
>      [    0.000000] Stack: c17eafa8 c17fd410 c16747bc c17eafc4 c17fd7e5 000011fd f8616000 c18237cc
>      [    0.000000]        00099800 c17bb000 c17eafec c17f1668 000001c5 c17f1322 c166e039 c1822bf0
>      [    0.000000]        c166e033 c153a014 c18237cc 00020800 c17eaff8 c17f106a 00020800 01ba5003
>      [    0.000000] Pid: 0, comm: swapper Not tainted 2.6.30-tip-02161-g7a74539-dirty #52203
>      [    0.000000] Call Trace:
>      [    0.000000]  [<c15357c2>] ? printk+0x14/0x16
>      [    0.000000]  [<c10135b1>] ? do_test_wp_bit+0x19/0x23
>      [    0.000000]  [<c17fd410>] ? test_wp_bit+0x26/0x64
>      [    0.000000]  [<c17fd7e5>] ? mem_init+0x1ba/0x1d8
>      [    0.000000]  [<c17f1668>] ? start_kernel+0x164/0x2f7
>      [    0.000000]  [<c17f1322>] ? unknown_bootoption+0x0/0x19c
>      [    0.000000]  [<c17f106a>] ? __init_begin+0x6a/0x6f
>
>    Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
>    Acked-by Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>    Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
>    Cc: Ingo Molnar <mingo@xxxxxxx>
>    Cc: Matt Mackall <mpm@xxxxxxxxxxx>
>    Cc: Nick Piggin <npiggin@xxxxxxx>
>    Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
>    Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
>
> However a
> git revert 83b519e8b9572c319c8e0c615ee5dd7272856090
> to verify that current git without that commit would work,
> didn't succeed right away, so I was not able to test that.

Thanks for doing the bisect! Can we also see your .config also?

I doubt this is a slab allocator initialization issue so I'm CC'ing
some Xen folks. Jeremy, I don't know Xen well but on quick read, the
only thing that I can see is that trap_init() is called before
sched_init() now. I see Xen doing preempt_enable()/preempt_disable so
maybe that's a problem now?

                                 Pekka
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