[PATCH net V2] net/mlx5e: Order ICOSQ cc update after CQ doorbell

[Tariq Toukan]

From: Li RongQing <lirongqing@xxxxxxxxx>

mlx5e_poll_ico_cq() requires sq->cc to be updated only after
mlx5_cqwq_update_db_record(), otherwise a CQ overrun may occur.

The current implementation updates sq->cc before the CQ doorbell
record, violating this ordering requirement.

Update the CQ doorbell record first and use dma_wmb() before updating
sq->cc. This ensures that the CQ space is released to the device
before the corresponding ICOSQ consumer index is updated by software.

Fixes: fd9b4be8002c ("net/mlx5e: RX, Support multiple outstanding UMR posts")
Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
Reviewed-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
Signed-off-by: Tariq Toukan <tariqt@xxxxxxxxxx>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

V2:
- Resending, after verified.

V1:
https://lore.kernel.org/all/20260820030821.1731-1-lirongqing@xxxxxxxxx/

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 7bd0606a5253..903af3b3e779 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -908,10 +908,12 @@ int mlx5e_poll_ico_cq(struct mlx5e_cq *cq)
 		} while (!last_wqe);
 	} while ((++i < MLX5E_TX_CQ_POLL_BUDGET) && (cqe = mlx5_cqwq_get_cqe(&cq->wq)));
 
-	sq->cc = sqcc;
-
 	mlx5_cqwq_update_db_record(&cq->wq);
 
+	/* ensure cq space is freed before enabling more cqes */
+	dma_wmb();
+
+	sq->cc = sqcc;
 	return i;
 }
 

base-commit: d5a007b9b457c915ab1a53227e8939e4018aa97a
-- 
2.44.0