Re: [dpdk-stable] [PATCH] net/mlx5: fix transmit descriptor with VLAN insertions

[Matan Azrad <matan@mellanox.com>]

Hi Slava

From: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
> If VLAN tag insertion transmit offload is engaged
> (DEV_TX_OFFLOAD_VLAN_INSERT in tx queue configuration is set) the
> transmit descriptor may be built with wrong format, due to packet length is
> not adjusted. Also, the ring buffer wrapup is not handled correctly.
> 
> Fixes: 18a1c20044c0 ("net/mlx5: implement Tx burst template")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
> ---
>  drivers/net/mlx5/mlx5_rxtx.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
> index 8ec90c3..f540977 100644
> --- a/drivers/net/mlx5/mlx5_rxtx.c
> +++ b/drivers/net/mlx5/mlx5_rxtx.c
> @@ -2861,13 +2861,14 @@ enum mlx5_txcmp_code {
>  	memcpy(pdst, buf, MLX5_DSEG_MIN_INLINE_SIZE);
>  	buf += MLX5_DSEG_MIN_INLINE_SIZE;
>  	pdst += MLX5_DSEG_MIN_INLINE_SIZE;
> +	len -= MLX5_DSEG_MIN_INLINE_SIZE;
>  	/* Insert VLAN ethertype + VLAN tag. Pointer is aligned. */
>  	assert(pdst == RTE_PTR_ALIGN(pdst, MLX5_WSEG_SIZE));
> +	if (unlikely(pdst >= (uint8_t *)txq->wqes_end))

Why unlikely?
Wraparound is expected even in good cases, no?



> +		pdst = (uint8_t *)txq->wqes;
>  	*(uint32_t *)pdst = rte_cpu_to_be_32((RTE_ETHER_TYPE_VLAN <<
> 16) |
>  					      loc->mbuf->vlan_tci);
>  	pdst += sizeof(struct rte_vlan_hdr);
> -	if (unlikely(pdst >= (uint8_t *)txq->wqes_end))
> -		pdst = (uint8_t *)txq->wqes;
>  	/*
>  	 * The WQEBB space availability is checked by caller.
>  	 * Here we should be aware of WQE ring buffer wraparound only.
> --
> 1.8.3.1