Re: [dpdk-dev] [PATCH 1/2] net/mlx4: fix memory barrier incorrectly placed

[Slava Ovsiienko <viacheslavo@nvidia.com>]

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Chengwen Feng
> Sent: Monday, May 10, 2021 15:06
> To: NBU-Contact-Thomas Monjalon <thomas@monjalon.net>;
> ferruh.yigit@intel.com
> Cc: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH 1/2] net/mlx4: fix memory barrier incorrectly
> placed
> 
> The memory barrier is used to ensure that the response is returned only
> after the Tx/Rx function is set, it should place after the Rx/Tx function is set.
> 
> Fixes: 0203d33a1059 ("net/mlx4: support secondary process")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>


Hi, Chengwen

Nice catch, thank you for the patches.
Just out of curiosity - did we meet the real issue with this ineffective barrier?

With best regards,
Slava

> ---
>  drivers/net/mlx4/mlx4_mp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/mlx4/mlx4_mp.c b/drivers/net/mlx4/mlx4_mp.c
> index ddf7bdb..8fcfb54 100644
> --- a/drivers/net/mlx4/mlx4_mp.c
> +++ b/drivers/net/mlx4/mlx4_mp.c
> @@ -126,7 +126,6 @@ mp_secondary_handle(const struct rte_mp_msg
> *mp_msg, const void *peer)
>  	switch (param->type) {
>  	case MLX4_MP_REQ_START_RXTX:
>  		INFO("port %u starting datapath", dev->data->port_id);
> -		rte_mb();
>  		dev->tx_pkt_burst = mlx4_tx_burst;
>  		dev->rx_pkt_burst = mlx4_rx_burst;
>  #ifdef HAVE_IBV_MLX4_UAR_MMAP_OFFSET
> @@ -144,6 +143,7 @@ mp_secondary_handle(const struct rte_mp_msg
> *mp_msg, const void *peer)
>  			}
>  		}
>  #endif
> +		rte_mb();
>  		mp_init_msg(dev, &mp_res, param->type);
>  		res->result = 0;
>  		ret = rte_mp_reply(&mp_res, peer);
> --
> 2.8.1