From: Gal Pressman <gal@nvidia.com>

mlx5e_tc_act_vlan_add_push_action() uses tail-recursion to walk through
a stack of VLAN devices.

There is no need for a complicated recursion with unnecessary stack
consumption and less obvious code flow, rewrite the function so that it
uses a do while loop instead.

Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
---
 .../mellanox/mlx5/core/en/tc/act/vlan.c       | 43 ++++++++++---------
 1 file changed, 22 insertions(+), 21 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/tc/act/vlan.c b/drivers/net/ethernet/mellanox/mlx5/core/en/tc/act/vlan.c
index a13c5e707b83..9bdb5820c553 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/tc/act/vlan.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/tc/act/vlan.c
@@ -94,29 +94,30 @@ mlx5e_tc_act_vlan_add_push_action(struct mlx5e_priv *priv,
 				  struct net_device **out_dev,
 				  struct netlink_ext_ack *extack)
 {
-	struct net_device *vlan_dev = *out_dev;
-	struct flow_action_entry vlan_act = {
-		.id = FLOW_ACTION_VLAN_PUSH,
-		.vlan.vid = vlan_dev_vlan_id(vlan_dev),
-		.vlan.proto = vlan_dev_vlan_proto(vlan_dev),
-		.vlan.prio = 0,
-	};
-	int err;
-
-	err = parse_tc_vlan_action(priv, &vlan_act, attr->esw_attr, &attr->action, extack, NULL);
-	if (err)
-		return err;
-
-	rcu_read_lock();
-	*out_dev = dev_get_by_index_rcu(dev_net(vlan_dev), dev_get_iflink(vlan_dev));
-	rcu_read_unlock();
-	if (!*out_dev)
-		return -ENODEV;
+	do {
+		struct net_device *vlan_dev = *out_dev;
+		struct flow_action_entry vlan_act = {
+			.id = FLOW_ACTION_VLAN_PUSH,
+			.vlan.vid = vlan_dev_vlan_id(vlan_dev),
+			.vlan.proto = vlan_dev_vlan_proto(vlan_dev),
+			.vlan.prio = 0,
+		};
+		int err;
+
+		err = parse_tc_vlan_action(priv, &vlan_act, attr->esw_attr,
+					   &attr->action, extack, NULL);
+		if (err)
+			return err;
 
-	if (is_vlan_dev(*out_dev))
-		err = mlx5e_tc_act_vlan_add_push_action(priv, attr, out_dev, extack);
+		rcu_read_lock();
+		*out_dev = dev_get_by_index_rcu(dev_net(vlan_dev),
+						dev_get_iflink(vlan_dev));
+		rcu_read_unlock();
+		if (!*out_dev)
+			return -ENODEV;
+	} while (is_vlan_dev(*out_dev));
 
-	return err;
+	return 0;
 }
 
 int
-- 
2.31.1

On Wed, 9 Jul 2025 00:16:25 +0300 Tariq Toukan wrote:
> +		rcu_read_lock();
> +		*out_dev = dev_get_by_index_rcu(dev_net(vlan_dev),
> +						dev_get_iflink(vlan_dev));
> +		rcu_read_unlock();
> +		if (!*out_dev)
> +			return -ENODEV;
> +	} while (is_vlan_dev(*out_dev));

Would be good adding a comment here to explain why this odd rcu lock
/ lookup / rcu unlock / keep using the return value outside of rcu
protection - code flow is correct :S

On Wed, Jul 09, 2025 at 12:16:25AM +0300, Tariq Toukan wrote:
> From: Gal Pressman <gal@nvidia.com>
> 
> mlx5e_tc_act_vlan_add_push_action() uses tail-recursion to walk through
> a stack of VLAN devices.
> 
> There is no need for a complicated recursion with unnecessary stack
> consumption and less obvious code flow, rewrite the function so that it
> uses a do while loop instead.
> 
> Signed-off-by: Gal Pressman <gal@nvidia.com>
> Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
> Signed-off-by: Tariq Toukan <tariqt@nvidia.com>

Reviewed-by: Simon Horman <horms@kernel.org>