Re: [dpdk-dev] [PATCH v2] raw/ntb: fix write memory barrier issue

[Gavin Hu (Arm Technology China)]

> -----Original Message-----
> From: dev <dev-boun...@dpdk.org> On Behalf Of Xiaoyun Li
> Sent: Monday, December 16, 2019 9:59 AM
> To: jingjing...@intel.com
> Cc: dev@dpdk.org; omkar.masle...@intel.com; Xiaoyun Li
> <xiaoyun...@intel.com>; sta...@dpdk.org
> Subject: [dpdk-dev] [PATCH v2] raw/ntb: fix write memory barrier issue
> 
> All buffers and ring info should be written before tail register update.
> This patch relocates the write memory barrier before updating tail register
> to avoid potential issues.
> 
> Fixes: 11b5c7daf019 ("raw/ntb: add enqueue and dequeue functions")
> Cc: sta...@dpdk.org
> 
> Signed-off-by: Xiaoyun Li <xiaoyun...@intel.com>
> ---
> v2:
>  * Replaced rte_wmb with rte_io_wmb since rte_io_wmb is enough.
> ---
>  drivers/raw/ntb/ntb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/raw/ntb/ntb.c b/drivers/raw/ntb/ntb.c
> index ad7f6abfd..c7de86f36 100644
> --- a/drivers/raw/ntb/ntb.c
> +++ b/drivers/raw/ntb/ntb.c
> @@ -683,8 +683,8 @@ ntb_enqueue_bufs(struct rte_rawdev *dev,
>                          sizeof(struct ntb_used) * nb1);
>               rte_memcpy(txq->tx_used_ring, tx_used + nb1,
>                          sizeof(struct ntb_used) * nb2);
> +             rte_io_wmb();
As both txq->tx_used_ring and *txq->used_cnt are physically reside in the PCI 
device side, rte_io_wmb is correct to ensure the ordering.

>               *txq->used_cnt = txq->last_used;
> -             rte_wmb();
> 
>               /* update queue stats */
>               hw->ntb_xstats[NTB_TX_BYTES_ID + off] += bytes;
> @@ -789,8 +789,8 @@ ntb_dequeue_bufs(struct rte_rawdev *dev,
>                          sizeof(struct ntb_desc) * nb1);
>               rte_memcpy(rxq->rx_desc_ring, rx_desc + nb1,
>                          sizeof(struct ntb_desc) * nb2);
> +             rte_io_wmb();
>               *rxq->avail_cnt = rxq->last_avail;
> -             rte_wmb();
> 
>               /* update queue stats */
>               off = NTB_XSTATS_NUM * ((size_t)context + 1);
> --
> 2.17.1

Reviewed-by: Gavin Hu <gavin...@arm.com>