[dpdk-stable] [dpdk-dev] [PATCH 2/2] malloc: fix realloc padded element size

[Burakov, Anatoly]

On 21-Nov-19 1:15 PM, Burakov, Anatoly wrote:
> On 21-Nov-19 12:55 PM, Xueming(Steven) Li wrote:
>> Hi Anatoly,
>>
>>> -----Original Message-----
>>> From: Burakov, Anatoly <anatoly.burakov at intel.com>
>>> Sent: Thursday, November 21, 2019 8:30 PM
>>> To: David Marchand <david.marchand at redhat.com>; Xueming(Steven) Li
>>> <xuemingl at mellanox.com>
>>> Cc: Asaf Penso <asafp at mellanox.com>; dev <dev at dpdk.org>; dpdk stable
>>> <stable at dpdk.org>
>>> Subject: Re: [dpdk-stable] [PATCH 2/2] malloc: fix realloc padded 
>>> element size
>>>
>>> On 20-Nov-19 1:25 PM, David Marchand wrote:
>>>> On Wed, Nov 20, 2019 at 3:12 AM Xueming(Steven) Li
>>>> <xuemingl at mellanox.com> wrote:
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: David Marchand <david.marchand at redhat.com>
>>>>>> Sent: Wednesday, November 20, 2019 4:47 AM
>>>>>> To: Xueming(Steven) Li <xuemingl at mellanox.com>; Anatoly Burakov
>>>>>> <anatoly.burakov at intel.com>
>>>>>> Cc: Asaf Penso <asafp at mellanox.com>; dev <dev at dpdk.org>; dpdk stable
>>>>>> <stable at dpdk.org>
>>>>>> Subject: Re: [dpdk-stable] [PATCH 2/2] malloc: fix realloc padded
>>>>>> element size
>>>>>>
>>>>>> On Tue, Nov 12, 2019 at 3:50 PM Xueming Li <xuemingl at mellanox.com>
>>>>>> wrote:
>>>>>>>
>>>>>>> When resize a memory with next element, the original element size 
>>>>>>> grows.
>>>>>>> If the orginal element has padding, the real inner element size
>>>>>>> didn't grow as well and this causes trailer verification failure
>>>>>>> when malloc debug enabled.
>>>>>>
>>>>>> I did not see this when running the malloc_autotest with debug 
>>>>>> enabled.
>>>>>> What is missing for me to catch it?
>>>>>>
>>>>> Yes, it happens rarely, depends on memory fragment. I only caught 
>>>>> this in
>>> middle of a long test.
>>>>>
>>>>>>
>>>>>> Just a bit chilly to apply this series.
>>>>>> The first patch seems an optimisation.
>>>>>> The second one seems more interesting if we fix the debug mode, but
>>>>>> I suppose we can live without them in 19.11.
>>>>> Few people enable memory debug option, they are there for years.
>>>>
>>>> Had a discussion offlist with Anatoly.
>>>> Those two issues are hard to catch but the fixes are relevant and
>>>> Anatoly is confident.
>>>> I will take this in rc3.
>>>>
>>>> Series applied, thanks.
>>>>
>>>
>>> To test them, i had to modify malloc to always create padded elements :)
>>
>> I fix another issue in element join, as I made some local enhancement 
>> patch on memory, it's required, not sure whether it help on public code.
>>
>> diff --git a/lib/librte_eal/common/malloc_elem.c 
>> b/lib/librte_eal/common/malloc_elem.c
>> index afacb1813c..c3fa0d1039 100644
>> --- a/lib/librte_eal/common/malloc_elem.c
>> +++ b/lib/librte_eal/common/malloc_elem.c
>> @@ -487,6 +487,10 @@ join_elem(struct malloc_elem *elem1, struct 
>> malloc_elem *elem2)
>>          else
>>                  elem1->heap->last = elem1;
>>          elem1->next = next;
>> +       if (elem1->pad) {
>> +               struct malloc_elem *inner = RTE_PTR_ADD(elem1, 
>> elem1->pad);
>> +               inner->size += elem2->size;
>> +       }
>>   }
>>
>>
> 
> This looks like a good change as well - while we /mostly/ join elements 
> when they're free, there is one case where we can join a free element 
> with one already occupied - and /that/ element could be padded, which we 
> currently don't update. So, this patch would help the public code as well.

(that said, the += should be replaced with explicit calculation of 
correct size, as this joining may be run multiple times, and we don't 
want incorrect size accumulating...)

> 
>>
>>>
>>> -- 
>>> Thanks,
>>> Anatoly
> 
> 


-- 
Thanks,
Anatoly