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Message-ID: <48517456.5000901@colorfullife.com>
Date: Thu, 12 Jun 2008 21:09:10 +0200
From: Manfred Spraul <manfred@...orfullife.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: Pekka J Enberg <penberg@...helsinki.fi>,
Nadia Derbey <Nadia.Derbey@...l.net>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Christoph Lameter <clameter@....com>
Subject: Re: repeatable slab corruption with LTP msgctl08
Andrew Morton wrote:
> On Thu, 12 Jun 2008 20:33:23 +0200 Manfred Spraul <manfred@...orfullife.com> wrote:
>
>
>> Pekka J Enberg wrote:
>>
>>> Hi Andrew,
>>>
>>> On Wed, 11 Jun 2008, Andrew Morton wrote:
>>>
>>>
>>>> version is ltp-full-20070228 (lots of retro-computing there).
>>>>
>>>> Config is at http://userweb.kernel.org/~akpm/config-vmm.txt
>>>>
>>>> ./testcases/bin/msgctl08 crashes after ten minutes or so:
>>>>
>>>> slab: Internal list corruption detected in cache 'size-128'(26), slabp f2905000(20). Hexdump:
>>>>
>>>> 000: 00 e0 12 f2 88 32 c0 f7 88 00 00 00 88 50 90 f2
>>>> 010: 14 00 00 00 0f 00 00 00 00 00 00 00 ff ff ff ff
>>>> 020: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
>>>> 030: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
>>>> 040: fd ff ff ff fd ff ff ff 00 00 00 00 fd ff ff ff
>>>> 050: fd ff ff ff fd ff ff ff 19 00 00 00 17 00 00 00
>>>> 060: fd ff ff ff fd ff ff ff 0b 00 00 00 fd ff ff ff
>>>> 070: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
>>>> 080: 10 00 00 00
>>>>
>>>>
>>> Looking at the above dump, slabp->free is 0x0f and the bufctl it points to
>>> is 0xff ("BUFCTL_END") which marks the last element in the chain. This is
>>> wrong as the total number of objects in the slab (cachep->num) is 26 but
>>> the number of objects in use (slabp->inuse) is 20. So somehow you have
>>> managed to lost 6 objects from the bufctl chain.
>>>
>>>
>>>
>> Hmm. double kfree() should be cached by the redzone code.
>> And I disagree with your link interpretation:
>>
>> 000: 00 e0 12 f2 88 32 c0 f7 88 00 00 00 88 50 90 f2
>> 010:
>> inuse: 14 00 00 00 (20 entries in use, 6 should be free)
>> free: 0f 00 00 00
>> nodeid: 00 00 00 00
>> bufctl[0x00] ff ff ff ff 020: fd ff ff ff fd ff ff ff fd ff ff ff
>> bufctl[0x4] fd ff ff ff 030: fd ff ff ff fd ff ff ff fd ff ff ff
>> bufctl[0x8] fd ff ff ff 040: fd ff ff ff fd ff ff ff 00 00 00 00
>> bufctl[0x0c] fd ff ff ff 050: fd ff ff ff fd ff ff ff 19 00 00 00
>> bufctl[0x10] 17 00 00 00 060: fd ff ff ff fd ff ff ff 0b 00 00 00
>> bufctl[0x14] fd ff ff ff 070: fd ff ff ff fd ff ff ff fd ff ff ff
>> bufctl[0x18] fd ff ff ff 080: 10 00 00 00
>>
>> free: points to entry 0x0f.
>> bufctl[0x0f] is 0x19, i.e. it points to entry 0x19
>> 0x19 points to 0x10
>> 0x10 points to 0x17
>> 0x17 is a BUFCTL_ACTIVE - that's a bug.
>> but: 0x13 is a valid link entry, is points to 0x0b
>> 0x0b points to 0x00, which is BUFCTL_END.
>>
>> IMHO the most probable bug is a single bit error:
>> bufctl[0x10] should be 0x13 instead of 0x17.
>>
>> What about printing all redzone words? That would allow us to validate the bufctl chain.
>>
>> Andrew: Could you post the new oops?
>>
>>
>
> umm, what new oops?
>
> I have four saved away here:
>
> slab: Internal list corruption detected in cache 'size-96'(32), slabp ea2a5040(28). Hexdump:
>
> 000: 20 90 b5 ec 88 54 80 f7 e0 00 00 00 e0 50 2a ea
> 010: 1c 00 00 00 17 00 00 00 00 00 00 00 fd ff ff ff
> 020: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
> 030: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
> 040: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
> 050: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
> 060: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
> 070: fd ff ff ff fd ff ff ff 18 00 00 00 1f 00 00 00
>
bufctl[0x18] 0x1b instead of 0x1f yields a valid bufctl chain.
> 080: fd ff ff ff fd ff ff ff 1c 00 00 00 ff ff ff ff
> 090: fd ff ff ff fd ff ff ff fd ff ff ff
> ------------[ cut here ]------------
> kernel BUG at mm/slab.c:2949!
> invalid opcode: 0000 [#1] SMP
> last sysfs file:
>
>
> slab: Internal list corruption detected in cache 'size-128'(26), slabp f2905000(20). Hexdump:
>
> 000: 00 e0 12 f2 88 32 c0 f7 88 00 00 00 88 50 90 f2
> 010: 14 00 00 00 0f 00 00 00 00 00 00 00 ff ff ff ff
> 020: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
> 030: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
> 040: fd ff ff ff fd ff ff ff 00 00 00 00 fd ff ff ff
> 050: fd ff ff ff fd ff ff ff 19 00 00 00 17 00 00 00
>
bufctl[0x10]: 0x13 instead of 0x17 creates a valid tree
> 060: fd ff ff ff fd ff ff ff 0b 00 00 00 fd ff ff ff
> 070: fd ff ff ff fd ff ff ff fd ff ff ff fd ff ff ff
> 080: 10 00 00 00
>
>
> slab: Internal list corruption detected in cache 'size-128'(26), slabp f7159000(18). Hexdump:
>
> 000: 00 f0 f8 f2 88 32 c0 f7 88 00 00 00 88 90 15 f7
> 010: 12 00 00 00 08 00 00 00 00 00 00 00
bufctl[0x00] 13 00 00 00 020: fd ff ff ff fd ff ff ff fd ff ff ff
bufctl[0x04] fd ff ff ff 030: 06 00 00 00 ff ff ff ff fd ff ff ff
bufctl[0x08] 18 00 00 00 040: fd ff ff ff fd ff ff ff 17 00 00 00
bufctl[0x0c] fd ff ff ff 050: fd ff ff ff fd ff ff ff fd ff ff ff
bufctl[0x10] fd ff ff ff 060: fd ff ff ff fd ff ff ff 05 00 00 00
bufctl[0x14] fd ff ff ff 070: fd ff ff ff fd ff ff ff 00 00 00 00
bufctl[0x18] 0f 00 00 00 080: fd ff ff ff
bufctl[0x18] is wrong, it must be 0x0b
> slab: Internal list corruption detected in cache 'size-128'(26), slabp ed9a9000(21). Hexdump:
>
> 000: 00 c0 3a f3 88 32 80 f7 88 00 00 00 88 90 9a ed
> 010: 15 00 00 00 12 00 00 00 00 00 00 00
bufcfl[0x00] fd ff ff ff 020: fd ff ff ff fd ff ff ff 07 00 00 00
bufctl[0x04] fd ff ff ff 030: fd ff ff ff fd ff ff ff 08 00 00 00
bufctl[0x08] 0f 00 00 00 040: fd ff ff ff fd ff ff ff ff ff ff ff
bufctl[0x0c] fd ff ff ff 050: fd ff ff ff fd ff ff ff fd ff ff ff
bufctl[0x10] fd ff ff ff 060: fd ff ff ff 03 00 00 00 fd ff ff ff
bufctl[0x14] fd ff ff ff 070: fd ff ff ff fd ff ff ff fd ff ff ff
bufctl[0x18 fd ff ff ff 080: fd ff ff ff
bufctl[0x08] is wrong, it must be 0x0b instead of 0x0f
> but they're all from under basically the same conditions.
>
All bugs appear to be a spurious 0x04 in a bufctl[nr%8==0].
Either someone does a set_bit() or your cpu is breaking down.
From looking at the the msgctl08 test: it shouldn't produce any races,
it just does lots of bulk msgsnd()/msgrcv() operations. Always one
thread sends, one thread receives on each queue. It's probably more a
scheduler stresstest than anything else.
Attached is a completely untested patch:
- add 8 bytes to each slabp struct: This changes the alignment of the
bufctl entries.
- add a hexdump of the redzone bytes. Andrew: how do you log the oops?
it might scroll of the screen.
--
Manfred
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