[PATCH net-next v2 3/3] mlx4: use READ_ONCE/WRITE_ONCE for ring indexes

[PATCH net-next v2 3/3] mlx4: use READ_ONCE/WRITE_ONCE for ring indexes

[Jakub Kicinski]

Eric points out that we should make sure that ring index updates
are wrapped in the appropriate READ_ONCE/WRITE_ONCE macros.

Suggested-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: tariqt@nvidia.com
CC: linux-rdma@vger.kernel.org
---
 drivers/net/ethernet/mellanox/mlx4/en_tx.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index 2f79378fbf6e..65cb63f6c465 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -228,7 +228,9 @@ void mlx4_en_deactivate_tx_ring(struct mlx4_en_priv *priv,
 
 static inline bool mlx4_en_is_tx_ring_full(struct mlx4_en_tx_ring *ring)
 {
-	return ring->prod - ring->cons > ring->full_size;
+	u32 used = READ_ONCE(ring->prod) - READ_ONCE(ring->cons);
+
+	return used > ring->full_size;
 }
 
 static void mlx4_en_stamp_wqe(struct mlx4_en_priv *priv,
@@ -1083,7 +1085,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
 			op_own |= cpu_to_be32(MLX4_WQE_CTRL_IIP);
 	}
 
-	ring->prod += nr_txbb;
+	WRITE_ONCE(ring->prod, ring->prod + nr_txbb);
 
 	/* If we used a bounce buffer then copy descriptor back into place */
 	if (unlikely(bounce))
@@ -1214,7 +1216,7 @@ netdev_tx_t mlx4_en_xmit_frame(struct mlx4_en_rx_ring *rx_ring,
 
 	rx_ring->xdp_tx++;
 
-	ring->prod += MLX4_EN_XDP_TX_NRTXBB;
+	WRITE_ONCE(ring->prod, ring->prod + MLX4_EN_XDP_TX_NRTXBB);
 
 	/* Ensure new descriptor hits memory
 	 * before setting ownership of this descriptor to HW
-- 
2.39.2

Re: [PATCH net-next v2 3/3] mlx4: use READ_ONCE/WRITE_ONCE for ring indexes

[Tariq Toukan]

On 12/04/2023 4:50, Jakub Kicinski wrote:
> Eric points out that we should make sure that ring index updates
> are wrapped in the appropriate READ_ONCE/WRITE_ONCE macros.
> 
> Suggested-by: Eric Dumazet <edumazet@google.com>
> Reviewed-by: Eric Dumazet <edumazet@google.com>
> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> CC: tariqt@nvidia.com
> CC: linux-rdma@vger.kernel.org
> ---
>   drivers/net/ethernet/mellanox/mlx4/en_tx.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 

Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Thanks!