Re: Boot problems on Malta with EVA (bisected to 12220dea07f1 "mm/slab: support slab merge")

[Markos Chandras]

On 10/28/2014 03:00 PM, Joonsoo Kim wrote:
> 2014-10-28 23:32 GMT+09:00 Markos Chandras <Markos.Chandras@xxxxxxxxxx>:
>> On 10/28/2014 02:21 PM, Joonsoo Kim wrote:
>>> 2014-10-28 22:48 GMT+09:00 Joonsoo Kim <js1304@xxxxxxxxx>:
>>>> 2014-10-28 22:24 GMT+09:00 Markos Chandras <Markos.Chandras@xxxxxxxxxx>:
>>>>> On 10/28/2014 01:19 PM, Markos Chandras wrote:
>>>>>> On 10/28/2014 01:01 PM, Joonsoo Kim wrote:
>>>>>>> 2014-10-28 19:45 GMT+09:00 Markos Chandras <Markos.Chandras@xxxxxxxxxx>:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> It seems I am unable to boot my Malta with EVA. The problem appeared in
>>>>>>>> the 3.18 merge window. I bisected the problem (between v3.17 and
>>>>>>>> v3.18-rc1) and I found the following commit responsible for the broken boot.
>>>>>>>
>>>>>>> Hello,
>>>>>>>
>>>>>>> Did you start to bisect from v3.18-rc1?
>>>>>>> I'd like to be sure that this is another bug which is fixed by following commit.
>>>>>>>
>>>>>>> commit 85c9f4b04a08f6bc770b77530c22d04103468b8f
>>>>>>> Author: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
>>>>>>> Date:   Mon Oct 13 15:51:01 2014 -0700
>>>>>>>
>>>>>>>     mm/slab: fix unaligned access on sparc64
>>>>>>>
>>>>>>> This fix is merged into v3.18-rc1 sometime later that
>>>>>>> 'support slab merge' is merged.
>>>>>>>
>>>>>>> Thanks.
>>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> I bisected from v3.17 until 3.18-rc1. But 3.18-rc2 and the latest
>>>>>> mainline (f7e87a44ef60ad379e39b45437604141453bf0ec) still have the same
>>>>>> problem
>>>>>>
>>>>>> btw i did more tests and this is not EVA specific. A maltaup_defconfig
>>>>>> fails in the same way. I suspect all malta*_defconfigs will fail in a
>>>>>> similar way which makes it probably easier for you to reproduce it on a
>>>>>> QEMU.
>>>>>>
>>>>>
>>>>> sorry maltaup_defconfig does not fail. maltasmvp_defconfig does. So it
>>>>> might be a similar problem like the one fixed in
>>>>> 85c9f4b04a08f6bc770b77530c22d04103468b8f
>>>>
>>>> Oops. Sorry. Above commit ('mm/slab: fix unaligned access on sparc64')
>>>> is irrelevant to this problem.
>>>>
>>>> Anyway, your problem would be related to merging with incompatible slab cache.
>>>> Best way to debug is printing source/target slab cache's object size and
>>>> alignment and find the problem. I will try to reproduce it using QEMU.
>>>
>>> I found that cross compile for MIPS isn't easy job. :)
>>
>> You could grab the following toolchain
>>
>> https://sourcery.mentor.com/GNUToolchain/release2791
>>
>> (get the IA32 linux tar)
>>
>> unpack it somewhere (eg /tmp) and then
>>
>> make ARCH=mips maltasmvp_defconfig
>> make ARCH=mips CROSS_COMPILE=/tmp/mips-2014.05/bin/mips-linux-gnu- -j8
>> or something :)
> 
> Wow!! Really Thanks!
> I will try it.
> 
>>> Could you help me to debug the problem with below patch?
>>
>> (there are a few build warnings with your patch
>> mm/slab.c:2065:4: warning: format '%lu' expects argument of type 'long
>> unsigned int', but argument 5 has type 'size_t' [-Wformat=]
>> mm/slab.c:2065:4: warning: format '%lu' expects argument of type 'long
>> unsigned int', but argument 7 has type 'unsigned int' [-Wformat=]
>> mm/slab.c:2065:4: warning: format '%lu' expects argument of type 'long
>> unsigned int', but argument 8 has type 'int' [-Wformat=]
>> mm/slab.c:2065:4: warning: format '%lu' expects argument of type 'long
>> unsigned int', but argument 9 has type 'int' [-Wformat=]
>> )
>>
>> but here is the output from a QEMU boot right before the crash
>>
>> CPU frequency 200.00 MHz
>> Calibrating delay loop... 1087.89 BogoMIPS (lpj=5439488)
>> pid_max: default: 32768 minimum: 301
>> __kmem_cache_alias: (cred_jar 92 0) to (kmalloc-128 128 128 128)
>> __kmem_cache_alias: (files_cache 256 0) to (kmalloc-256 256 128 256)
>> __kmem_cache_alias: (fs_cache 36 0) to (pid 64 64 44)
>> __kmem_cache_alias: (names_cache 4096 0) to (kmalloc-4096 4096 128 4096)
>> __kmem_cache_alias: (mnt_cache 160 0) to (filp 192 64 160)
>> Mount-cache hash table entries: 4096 (order: 0, 16384 bytes)
>> Mountpoint-cache hash table entries: 4096 (order: 0, 16384 bytes)
>> __kmem_cache_alias: (pool_workqueue 256 256) to (kmalloc-256 256 128 256)
> 
> alignment is mismatch between pool_workqueue and kmalloc-256,
> but, slab caches are merged, because they have same object size.
> Perhaps, slab cache for pool_workqueue returns 128 byte aligned memory
> and workqueue can't work well with it.
> 
> Quick fix may be something like below, but, I will try it on QEMU MIPS.
> 
> Thanks.
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 3a6e0cf..d57b1a2 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -269,6 +269,9 @@ struct kmem_cache *find_mergeable(size_t size, size_t align,
>                 if (s->size - size >= sizeof(void *))
>                         continue;
> 
> +               if (align > s->align)
> +                       continue;
> +
>                 return s;
>         }
>         return NULL;
> 
Hi,

Yeah this makes the kernel boot again.

-- 
markos
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