net/mlx5: Lag, multipath, give priority for routes with smaller network prefix

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: ad11c4f ("net/mlx5e: Lag, Only handle events from highest priority multipath entry")
Signed-off-by: Patrisious Haddad <[email protected]>
Signed-off-by: Mark Bloch <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: PatrisiousHaddad

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);