netdev - [net v2 7/7] net/mlx5e: Fix incorrect access of RCU-protected xdp

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Message-ID: <20201105202129.23644-8-saeedm@nvidia.com>
Date:   Thu, 5 Nov 2020 12:21:29 -0800
From:   Saeed Mahameed <saeedm@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>,
        "Maxim Mikityanskiy" <maximmi@...lanox.com>,
        Tariq Toukan <tariqt@...dia.com>,
        "Saeed Mahameed" <saeedm@...dia.com>
Subject: [net v2 7/7] net/mlx5e: Fix incorrect access of RCU-protected xdp_prog

From: Maxim Mikityanskiy <maximmi@...lanox.com>

rq->xdp_prog is RCU-protected and should be accessed only with
rcu_access_pointer for the NULL check in mlx5e_poll_rx_cq.

rq->xdp_prog may change on the fly only from one non-NULL value to
another non-NULL value, so the checks in mlx5e_xdp_handle and
mlx5e_poll_rx_cq will have the same result during one NAPI cycle,
meaning that no additional synchronization is needed.

Fixes: fe45386a2082 ("net/mlx5e: Use RCU to protect rq->xdp_prog")
Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
Reviewed-by: Tariq Toukan <tariqt@...dia.com>
Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 599f5b5ebc97..6628a0197b4e 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -1584,7 +1584,7 @@ int mlx5e_poll_rx_cq(struct mlx5e_cq *cq, int budget)
 	} while ((++work_done < budget) && (cqe = mlx5_cqwq_get_cqe(cqwq)));
 
 out:
-	if (rq->xdp_prog)
+	if (rcu_access_pointer(rq->xdp_prog))
 		mlx5e_xdp_rx_poll_complete(rq);
 
 	mlx5_cqwq_update_db_record(cqwq);
-- 
2.26.2