net/mlx5e: Do not produce metadata freelist entries in Tx port ts WQE xmit

Free Tx port timestamping metadata entries in the NAPI poll context and
consume metadata enties in the WQE xmit path. Do not free a Tx port
timestamping metadata entry in the WQE xmit path even in the error path to
avoid a race between two metadata entry producers.

Fixes: 3178308 ("net/mlx5e: Make tx_port_ts logic resilient to out-of-order CQEs")
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/r/20240409190820.227554-10-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Binary-Eater

drivers/net/ethernet/mellanox/mlx5/core/en/ptp.h

@@ -95,9 +95,15 @@ static inline void mlx5e_ptp_metadata_fifo_push(struct mlx5e_ptp_metadata_fifo *
 }
 
 static inline u8
+mlx5e_ptp_metadata_fifo_peek(struct mlx5e_ptp_metadata_fifo *fifo)
+{
+	return fifo->data[fifo->mask & fifo->cc];
+}
+
+static inline void
 mlx5e_ptp_metadata_fifo_pop(struct mlx5e_ptp_metadata_fifo *fifo)
 {
-	return fifo->data[fifo->mask & fifo->cc++];
+	fifo->cc++;
 }
 
 static inline void

drivers/net/ethernet/mellanox/mlx5/core/en_tx.c

@@ -398,6 +398,8 @@ mlx5e_txwqe_complete(struct mlx5e_txqsq *sq, struct sk_buff *skb,
 		     (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP))) {
 		u8 metadata_index = be32_to_cpu(eseg->flow_table_metadata);
 
+		mlx5e_ptp_metadata_fifo_pop(&sq->ptpsq->metadata_freelist);
+
 		mlx5e_skb_cb_hwtstamp_init(skb);
 		mlx5e_ptp_metadata_map_put(&sq->ptpsq->metadata_map, skb,
 					   metadata_index);
@@ -496,9 +498,6 @@ mlx5e_sq_xmit_wqe(struct mlx5e_txqsq *sq, struct sk_buff *skb,
 
 err_drop:
 	stats->dropped++;
-	if (unlikely(sq->ptpsq && (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)))
-		mlx5e_ptp_metadata_fifo_push(&sq->ptpsq->metadata_freelist,
-					     be32_to_cpu(eseg->flow_table_metadata));
 	dev_kfree_skb_any(skb);
 	mlx5e_tx_flush(sq);
 }
@@ -657,7 +656,7 @@ static void mlx5e_cqe_ts_id_eseg(struct mlx5e_ptpsq *ptpsq, struct sk_buff *skb,
 {
 	if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP))
 		eseg->flow_table_metadata =
-			cpu_to_be32(mlx5e_ptp_metadata_fifo_pop(&ptpsq->metadata_freelist));
+			cpu_to_be32(mlx5e_ptp_metadata_fifo_peek(&ptpsq->metadata_freelist));
 }
 
 static void mlx5e_txwqe_build_eseg(struct mlx5e_priv *priv, struct mlx5e_txqsq *sq,