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

[David Marchand <david.marchand@redhat.com>]

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.


-- 
David Marchand