Re: [dpdk-dev] [PATCH v3] rte_ethdev: safer memory access by calling Rx/Tx callback

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 3/11/2020 12:26 PM, Jerin Jacob wrote:
> On Wed, Mar 11, 2020 at 5:52 PM Ananyev, Konstantin
> <konstantin.ananyev@intel.com> wrote:
>>
>>
>>
>>> -----Original Message-----
>>> From: ZY Qiu <quzeyao@gmail.com>
>>> Sent: Thursday, March 5, 2020 4:47 PM
>>> To: Thomas Monjalon <thomas@monjalon.net>; Yigit, Ferruh <ferruh.yigit@intel.com>; Andrew Rybchenko <arybchenko@solarflare.com>
>>> Cc: dev@dpdk.org; stephen@networkplumber.org; Ananyev, Konstantin <konstantin.ananyev@intel.com>; ZY Qiu
>>> <tgw_team@tencent.com>
>>> Subject: [PATCH v3] rte_ethdev: safer memory access by calling Rx/Tx callback
>>>
>>> When compiling with -O0,
>>> the compiler does not optimize two memory accesses into one.
>>> Leads to accessing a null pointer when queue post Rx burst callback
>>> removal while traffic is running.
>>>
>>> Signed-off-by: ZY Qiu <tgw_team@tencent.com>
>>> ---
>>>   lib/librte_ethdev/rte_ethdev.h | 9 +++++----
>>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
>>> index d1a593ad1..c46612e3e 100644
>>> --- a/lib/librte_ethdev/rte_ethdev.h
>>> +++ b/lib/librte_ethdev/rte_ethdev.h
>>> @@ -4388,10 +4388,10 @@ rte_eth_rx_burst(uint16_t port_id, uint16_t queue_id,
>>>                                     rx_pkts, nb_pkts);
>>>
>>>   #ifdef RTE_ETHDEV_RXTX_CALLBACKS
>>> -     if (unlikely(dev->post_rx_burst_cbs[queue_id] != NULL)) {
>>> -             struct rte_eth_rxtx_callback *cb =
>>> -                             dev->post_rx_burst_cbs[queue_id];
>>> +     struct rte_eth_rxtx_callback *volatile cb =
>>> +                     dev->post_rx_burst_cbs[queue_id];
> 
> I prefer to change to compiler_barrier() if it working as volatile may have a
> performance impact on fast-path code.
> 

Hi ZY Qiu,

Did you able to test with compiler barrier, is it solving your problem?

If there is no update on the issue, I will mark it as rejected.

Thanks,
ferruh


> 
>>>
>>> +     if (unlikely(cb != NULL)) {
>>>                do {
>>>                        nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts, nb_rx,
>>>                                                nb_pkts, cb->param);
>>> @@ -4652,7 +4652,8 @@ rte_eth_tx_burst(uint16_t port_id, uint16_t queue_id,
>>>   #endif
>>>
>>>   #ifdef RTE_ETHDEV_RXTX_CALLBACKS
>>> -     struct rte_eth_rxtx_callback *cb = dev->pre_tx_burst_cbs[queue_id];
>>> +     struct rte_eth_rxtx_callback *volatile cb =
>>> +                     dev->pre_tx_burst_cbs[queue_id];
>>>
>>>        if (unlikely(cb != NULL)) {
>>>                do {
>>> --
>>
>> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
>>
>>> 2.17.1
>>