Re: mem_cgroup_page_lruvec: BUG: unable to handle kernel NULL pointer dereference at 00000000000001a8

[Richard Weinberger <richard@nod.at>]

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Am 13.06.2013 15:32, schrieb Michal Hocko:
> Ohh and could you post the config please? Sorry should have asked
> earlier.

See attachment.

> On Thu 13-06-13 15:29:08, Michal Hocko wrote:
>>
>> On Thu 13-06-13 14:06:20, Richard Weinberger wrote:
>> [...]
>>> All code
>>> ========
>>>     0:   89 50 08                mov    %edx,0x8(%rax)
>>>     3:   48 89 d1                mov    %rdx,%rcx
>>>     6:   0f 1f 40 00             nopl   0x0(%rax)
>>>     a:   49 8b 04 24             mov    (%r12),%rax
>>>     e:   48 89 c2                mov    %rax,%rdx
>>>    11:   48 c1 e8 38             shr    $0x38,%rax
>>>    15:   83 e0 03                and    $0x3,%eax
>> 					nid = page_to_nid
>>>    18:   48 c1 ea 3a             shr    $0x3a,%rdx
>> 					zid = page_zonenum
>>
>>>    1c:   48 69 c0 38 01 00 00    imul   $0x138,%rax,%rax
>>>    23:   48 03 84 d1 e0 02 00    add    0x2e0(%rcx,%rdx,8),%rax
>> 					&memcg->nodeinfo[nid]->zoneinfo[zid]
>>
>>>    2a:   00
>>>    2b:*  48 3b 58 70             cmp    0x70(%rax),%rbx     <-- trapping instruction
>>
>> OK, so this maps to:
>>          if (unlikely(lruvec->zone != zone)) <<<
>>                  lruvec->zone = zone;
>>
>>> [35355.883056] RSP: 0000:ffff88003d523aa8  EFLAGS: 00010002
>>> [35355.883056] RAX: 0000000000000138 RBX: ffff88003fffa600 RCX: ffff88003e04a800
>>> [35355.883056] RDX: 0000000000000020 RSI: 0000000000000000 RDI: 0000000000028500
>>> [35355.883056] RBP: ffff88003d523ab8 R08: 0000000000000000 R09: 0000000000000000
>>> [35355.883056] R10: 0000000000000000 R11: dead000000100100 R12: ffffea0000a14000
>>> [35355.883056] R13: ffff88003e04b138 R14: ffff88003d523bb8 R15: ffffea0000a14020
>>> [35355.883056] FS:  0000000000000000(0000) GS:ffff88003fd80000(0000)
>>
>> RAX (lruvec) is obviously incorrect and it doesn't make any sense. rax should
>> contain an address at an offset from ffff88003e04a800 But there is 0x138 there
>> instead.
>>
>> Is this easily reproducible? Could you configure kdump.

Not really. So far it happened only once...

Thanks,
//richard


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