mlxsw: spectrum_router: Avoid expensive lookup during route removal

In commit fc922bb0 ("mlxsw: spectrum_router: Use one LPM tree for
all virtual routers") I increased the scale of supported VRFs by having
all of them share the same LPM tree.

In order to avoid look-ups for prefix lengths that don't exist, each
route removal would trigger an aggregation across all the active virtual
routers to see which prefix lengths are in use and which aren't and
structure the tree accordingly.

With the way the data structures are currently laid out, this is a very
expensive operation. When preformed repeatedly - due to the invocation
of the abort mechanism - and with enough VRFs, this can result in a hung
task.

For now, avoid this optimization until it can be properly re-added in
net-next.

Fixes: fc922bb0 ("mlxsw: spectrum_router: Use one LPM tree for all virtual routers")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reported-by: David Ahern <dsa@cumulusnetworks.com>
Tested-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c

@@ -3505,20 +3505,6 @@ static int mlxsw_sp_fib_lpm_tree_link(struct mlxsw_sp *mlxsw_sp,
 static void mlxsw_sp_fib_lpm_tree_unlink(struct mlxsw_sp *mlxsw_sp,
 					 struct mlxsw_sp_fib *fib)
 {
-	struct mlxsw_sp_prefix_usage req_prefix_usage = {{ 0 } };
-	struct mlxsw_sp_lpm_tree *lpm_tree;
-
-	/* Aggregate prefix lengths across all virtual routers to make
-	 * sure we only have used prefix lengths in the LPM tree.
-	 */
-	mlxsw_sp_vrs_prefixes(mlxsw_sp, fib->proto, &req_prefix_usage);
-	lpm_tree = mlxsw_sp_lpm_tree_get(mlxsw_sp, &req_prefix_usage,
-					 fib->proto);
-	if (IS_ERR(lpm_tree))
-		goto err_tree_get;
-	mlxsw_sp_vrs_lpm_tree_replace(mlxsw_sp, fib, lpm_tree);
-
-err_tree_get:
 	if (!mlxsw_sp_prefix_usage_none(&fib->prefix_usage))
 		return;
 	mlxsw_sp_vr_lpm_tree_unbind(mlxsw_sp, fib);