selftests: devlink_trap_l3_drops: Avoid race condition

The test checks that packets are trapped when they should egress a
router interface (RIF) that has become disabled. This is a temporary
state in a RIF's deletion sequence.

Currently, the test deletes the RIF by flushing all the IP addresses
configured on the associated netdev (br0). However, this is racy, as
this also flushes all the routes pointing to the netdev and if the
routes are deleted from the device before the RIF is disabled, then no
packets will try to egress the disabled RIF and the trap will not be
triggered.

Instead, trigger the deletion of the RIF by unlinking the mlxsw port
from the bridge that is backing the RIF. Unlike before, this will not
cause the kernel to delete the routes pointing to the bridge.

Note that due to current mlxsw locking scheme the RIF is always deleted
first, but this is going to change.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/drivers/net/mlxsw/devlink_trap_l3_drops.sh

@@ -641,13 +641,9 @@ erif_disabled_test()
 	mz_pid=$!
 
 	sleep 5
-	# In order to see this trap we need a route that points to disabled RIF.
-	# When ipv6 address is flushed, there is a delay and the routes are
-	# deleted before the RIF and we cannot get state that we have route
-	# to disabled RIF.
-	# Delete IPv6 address first and then check this trap with flushing IPv4.
-	ip -6 add flush dev br0
-	ip -4 add flush dev br0
+	# Unlinking the port from the bridge will disable the RIF associated
+	# with br0 as it is no longer an upper of any mlxsw port.
+	ip link set dev $rp1 nomaster
 
 	t1_packets=$(devlink_trap_rx_packets_get $trap_name)
 	t1_bytes=$(devlink_trap_rx_bytes_get $trap_name)
@@ -659,7 +655,6 @@ erif_disabled_test()
 	log_test "Egress RIF disabled"
 
 	kill $mz_pid && wait $mz_pid &> /dev/null
-	ip link set dev $rp1 nomaster
 	__addr_add_del $rp1 add 192.0.2.2/24 2001:db8:1::2/64
 	ip link del dev br0 type bridge
 	devlink_trap_action_set $trap_name "drop"