Re: [PATCH net-next 5/9] sunvnet: add memory barrier before check for tx enable

[Eric Dumazet]

On Fri, 2017-02-03 at 09:42 -0800, Shannon Nelson wrote:
> In order to allow the underlying LDC and outstanding memory operations
> to potentially catch up with the driver's Tx requests, add a memory
> barrier before checking again for available tx descriptors.
> 
> Signed-off-by: Shannon Nelson <shannon.nel...@oracle.com>
> ---
>  drivers/net/ethernet/sun/sunvnet_common.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sun/sunvnet_common.c 
> b/drivers/net/ethernet/sun/sunvnet_common.c
> index 5d0d386..98e758e 100644
> --- a/drivers/net/ethernet/sun/sunvnet_common.c
> +++ b/drivers/net/ethernet/sun/sunvnet_common.c
> @@ -1467,6 +1467,7 @@ ldc_start_done:
>       dr->prod = (dr->prod + 1) & (VNET_TX_RING_SIZE - 1);
>       if (unlikely(vnet_tx_dring_avail(dr) < 1)) {
>               netif_tx_stop_queue(txq);
> +             dma_wmb();

This does not look right.

I believe you need smp_rmb() here.

>               if (vnet_tx_dring_avail(dr) > VNET_TX_WAKEUP_THRESH(dr))
>                       netif_tx_wake_queue(txq);
>       }