Re: [dpdk-dev] Memory allocated using rte_zmalloc() has non-zeros

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 18.07.2018 20:18, Burakov, Anatoly wrote:
> On 18-Jul-18 4:20 PM, Andrew Rybchenko wrote:
>> Hi Anatoly,
>>
>> I'm investigating issue which finally comes to the fact that memory 
>> allocated using
>> rte_zmalloc() has non zeros.
>>
>> If I add memset just after allocation, everything is perfect and 
>> works fine.
>>
>> I've found out that memset was removed from rte_zmalloc_socket() some 
>> time ago:
>>
>>  >>>
>> commit b78c9175118f7d61022ddc5c62ce54a1bd73cea5
>> Author: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>
>> Date:   Tue Jul 5 12:01:16 2016 +0100
>>
>>      mem: do not zero out memory on zmalloc
>>
>>      Zeroing out memory on rte_zmalloc_socket is not required anymore 
>> since all
>>      allocated memory is already zeroed.
>>
>>      Signed-off-by: Sergio Gonzalez Monroy 
>> <sergio.gonzalez.monroy@intel.com>
>> <<<
>>
>> but may be something has changed now that made above statement false.
>>
>> I observe the problem when memory is reallocated. I.e. I configure 7 
>> queues,
>> start, stop, reconfigure to 3 queues, start. Memory is allocated on 
>> start and
>> freed on stop, since we have less queues on the second start it is 
>> allocated
>> in a different way and reuses previously allocated/freed memory.
>>
>> Do you have any ideas what could be wrong?
>>
>> Andrew.
>>
>>
>
> Hi Andrew,
>
> I will look into it first thing tomorrow. In general, we memset(0) on 
> free, and kernel gives us zeroed out pages initially, so the most 
> likely point of failure is that i'm not overwring some malloc headers 
> correctly on free.

OK, at least now I know how it is supposed to work in theory.

The following region was allocated  (the second number below is pointer 
plus size)
ALLOC 0x7fffa3264080-0x7fffa32640b8

Not zerod address is 16 bytes before:
(gdb) p/x ((uint64_t *)0x7fffa3264070)[0]
$4 = 0x4000000002
(gdb) p/x ((uint64_t  *)0x7fffa3264070)[1]
$5 = 0x80

then freed
FREE 0x7fffa3264080-0x7fffa32640b8

but above values (gdb) are still the same
then it is allocated as the part of bigger memory chunk
ALLOC 0x7fffa3245b80-0x7fffa3265fd8
which should contain zeros, but above values are still the same.

It is interesting that it looks like it was the first block freed on the 
port stop. I'm not 100% sure since I've put printouts to my allocation 
wrapper, not EAL.

Many thanks,
Andrew.