Re: [dpdk-dev] [PATCH dpdk-dev] rte_random: fix crash when random init

["Mattias Rönnblom" <mattias.ronnblom@ericsson.com>]

On 2020-04-15 01:42, Tonghao Zhang wrote:
> On Tue, Apr 14, 2020 at 11:37 PM Mattias Rönnblom
> <mattias.ronnblom@ericsson.com> wrote:
>> On 2020-04-14 15:35, David Marchand wrote:
>>> On Tue, Apr 14, 2020 at 3:20 PM Mattias Rönnblom
>>> <mattias.ronnblom@ericsson.com> wrote:
>>>> On 2020-04-14 06:43, Tonghao Zhang wrote:
>>>>> On Tue, Apr 14, 2020 at 12:07 PM Stephen Hemminger
>>>>> <stephen@networkplumber.org> wrote:
>>>>>> On Sun, 12 Apr 2020 16:27:53 +0800
>>>>>> xiangxia.m.yue@gmail.com wrote:
>>>>>>
>>>>>>> From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
>>>>>>>
>>>>>>> When rte_rand_init is invoked, and the kernel
>>>>>>> (kernel version < 3.17) running dpdk does't support
>>>>>>> *getentropy, at the same time, the cpu does't support
>>>>>>> rdseed, the rte_rand_init will invoke rte_get_timer_cycles
>>>>>>> which function will invoke rte_get_hpet_cycles
>>>>>>> (RTE_LIBEAL_USE_HPET was enabled) while *eal_hpet is not
>>>>>>> allocated.
>>>>>>>
>>>>>>> Fixes: faf8fd252785 ("eal: improve entropy for initial PRNG seed")
>>>>>>> Fixes: 3f002f069612 ("eal: replace libc-based random generation with LFSR")
>>>>>>>
>>>>>>> Cc: stable@dpdk.org
>>>>>>>
>>>>>>> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
>>>>>> Are you sure this patch won't change current default to use HPET (which is slower)?
>>>>> In rte_eal_timer_init (linux/eal_timer.c)， it will set
>>>>> eal_timer_source = EAL_TIMER_TSC too.
>>>>> So after rte_eal_init, eal_timer_source == EAL_TIMER_TSC which is the
>>>>> default timer source actually.
>>>>> Then this patch will affect RTE_INIT function which invoke
>>>>> rte_get_timer_cycles. but hpet is not available yet.
>>>> Would using rte_rdtsc() directly be an option?
>>> s/rte_rdtsc/rte_get_tsc_cycles/
>>>
>>> This could work, but I am a bit surprised to see an initialisation in
>>> a constructor.
>>> The commitlog that moved rte_srand() from rte_eal_init does not
>>> explain why it was moved.
>>>
>>>
>> The initialization (i.e. automatic seeding) grew in complexity somewhat,
>> and with the new rte_random.c file, it felt like it would have a good,
>> new home.
>>
>>
>> That said, maybe it would have been better to add an initialization
>> function to the rte_random.h API, and have it called from
>> rte_eal_init(), to avoid the ordering issues with constructors.
> If we use that solution  we can register a callback which invoked when
> almost resources are  available:
> http://patches.dpdk.org/patch/68313/


We might then instead have a new ordering issue, if we wait too long 
with rte_random initialization, since other initialization code might 
well use rte_rand(). It seems like the memory heap expansion code does 
currently. rte_rand() is a pretty basic function, that should be safe to 
call early during initialization, I think.


I would suggest first switching to rte_get_tsc_cycles() and later 
potentially change to explicit (i.e. non-constructor), early, rte_random 
initialization.


>> Yet
>> another alternative would be to just move the seeding logic.
>>
>>
>