netdev - [PATCH net 1/5] net/mlx5: Lag, multipath, give priority for routes with smaller network prefix

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Message-ID: <20251225132717.358820-2-mbloch@nvidia.com>
Date: Thu, 25 Dec 2025 15:27:13 +0200
From: Mark Bloch <mbloch@...dia.com>
To: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David
 S. Miller" <davem@...emloft.net>
CC: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
	Tariq Toukan <tariqt@...dia.com>, Mark Bloch <mbloch@...dia.com>,
	<netdev@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Gal Pressman <gal@...dia.com>, "Patrisious
 Haddad" <phaddad@...dia.com>
Subject: [PATCH net 1/5] net/mlx5: Lag, multipath, give priority for routes with smaller network prefix

From: Patrisious Haddad <phaddad@...dia.com>

Today multipath offload is controlled by a single route and the route
controlling is selected if it meets one of the following criteria:
        1. No controlling route is set.
        2. New route destination is the same as old one.
        3. New route metric is lower than old route metric.

This can cause unwanted behaviour in case a new route is added
with a smaller network prefix which should get the priority.

Fix this by adding a new criteria to give priority to new route with
a smaller network prefix.

Fixes: ad11c4f1d8fd ("net/mlx5e: Lag, Only handle events from highest priority multipath entry")
Signed-off-by: Patrisious Haddad <phaddad@...dia.com>
Signed-off-by: Mark Bloch <mbloch@...dia.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/lag/mp.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lag/mp.c b/drivers/net/ethernet/mellanox/mlx5/core/lag/mp.c
index aee17fcf3b36..cdc99fe5c956 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lag/mp.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lag/mp.c
@@ -173,10 +173,15 @@ static void mlx5_lag_fib_route_event(struct mlx5_lag *ldev, unsigned long event,
 	}
 
 	/* Handle multipath entry with lower priority value */
-	if (mp->fib.mfi && mp->fib.mfi != fi &&
+	if (mp->fib.mfi &&
 	    (mp->fib.dst != fen_info->dst || mp->fib.dst_len != fen_info->dst_len) &&
-	    fi->fib_priority >= mp->fib.priority)
+	    mp->fib.dst_len <= fen_info->dst_len &&
+	    !(mp->fib.dst_len == fen_info->dst_len &&
+	      fi->fib_priority < mp->fib.priority)) {
+		mlx5_core_dbg(ldev->pf[idx].dev,
+			      "Multipath entry with lower priority was rejected\n");
 		return;
+	}
 
 	nh_dev0 = mlx5_lag_get_next_fib_dev(ldev, fi, NULL);
 	nh_dev1 = mlx5_lag_get_next_fib_dev(ldev, fi, nh_dev0);
-- 
2.34.1