[PATCH net] net/mlx5e: Update netdev features only after a successful ringparam set

[Dimitri Daskalakis <dimitri.daskalakis1@gmail.com>]

From: Dimitri Daskalakis <daskald@meta.com>

mlx5 couples HW-GRO with tcp-data-split. If a user sets rx-gro-hw on ->
tcp-data-split on -> rx-gro-hw off, the driver will leave HW-GRO on.
mlx5e_ethtool_set_tcp_data_split() calls netdev_update_features() when
tcp-data-split goes from enabled to disabled in case HW-GRO needs to be
released. mlx5e_fix_features() reads the new HDS config from
dev->cfg_pending, so HW-GRO is released before all ring parameters are
validated.

If the subsequent call to mlx5e_ethtool_set_ringparam() fails, the
ethtool core discards the pending change and reports tcp-data-split
enabled. The device is no longer splitting, and subsequent ring changes
are blocked.

Move the call to netdev_update_features() after
mlx5e_ethtool_set_ringparam() exits successfully.

The issue was discovered by manual code inspection during review of
a change that stops mlx5 users from disabling tcp-data-split. It was
reproduced on a ConnectX-7 with ethtool alone.

Steps to reproduce:
ethtool -K eth0 rx-gro-hw on
ethtool -G eth0 tcp-data-split on
ethtool -K eth0 rx-gro-hw off # HW-GRO kept on for tcp-data-split

ethtool -G eth0 tcp-data-split off rx 1 # de-sync driver & kernel state
 netlink error: mlx5_core: rx (1) < min (16)
 netlink error: Invalid argument

ethtool -G eth0 rx 1024 # valid ring changes are now blocked
 netlink error: mlx5_core: TCP-data-split is not supported when GRO HW is disabled
 netlink error: Invalid argument

This is not a terminal state, users can recover by setting rx-gro-hw on.
With the fix, the failing ringparam set leaves rx-gro-hw on and later
ring changes succeed.

Fixes: 46bcce5dfd33 ("net/mlx5e: Support ethtool tcp-data-split settings")
Reported-by: Björn Töpel <bjorn@kernel.org>
Closes: https://lore.kernel.org/87se2grw3d.fsf@all.your.base.are.belong.to.us/
Signed-off-by: Dimitri Daskalakis <daskald@meta.com>
---
 .../ethernet/mellanox/mlx5/core/en_ethtool.c    | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c b/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
index 3ed59ced0407..f38e033ab8fa 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
@@ -403,11 +403,6 @@ static bool mlx5e_ethtool_set_tcp_data_split(struct mlx5e_priv *priv,
 		return false;
 	}
 
-	/* Might need to disable HW-GRO if it was kept on due to hds. */
-	if (tcp_data_split == ETHTOOL_TCP_DATA_SPLIT_DISABLED &&
-	    dev->cfg->hds_config == ETHTOOL_TCP_DATA_SPLIT_ENABLED)
-		netdev_update_features(priv->netdev);
-
 	return true;
 }
 
@@ -468,13 +463,23 @@ static int mlx5e_set_ringparam(struct net_device *dev,
 			       struct netlink_ext_ack *extack)
 {
 	struct mlx5e_priv *priv = netdev_priv(dev);
+	int err;
 
 	if (!mlx5e_ethtool_set_tcp_data_split(priv,
 					      kernel_param->tcp_data_split,
 					      extack))
 		return -EINVAL;
 
-	return mlx5e_ethtool_set_ringparam(priv, param, extack);
+	err = mlx5e_ethtool_set_ringparam(priv, param, extack);
+	if (err)
+		return err;
+
+	/* Might need to disable HW-GRO if it was kept on due to hds. */
+	if (kernel_param->tcp_data_split == ETHTOOL_TCP_DATA_SPLIT_DISABLED &&
+	    dev->cfg->hds_config == ETHTOOL_TCP_DATA_SPLIT_ENABLED)
+		netdev_update_features(priv->netdev);
+
+	return 0;
 }
 
 void mlx5e_ethtool_get_channels(struct mlx5e_priv *priv,
-- 
2.52.0