[PATCH net 0/3] Always flood multicast to the DSA CPU port

Discussing with Qingfang, it became obvious that DSA is not prepared to
disable multicast flooding towards the CPU port under any circumstance
right now, and this in fact breaks traffic quite blatantly.

This series is a revert done in reverse chronological order. These
should be propagated to stable trees up to commit a8b659e7ff75 ("net:
dsa: act as passthrough for bridge port flags") which is in v5.12.
For older kernels, that commit blocks further backporting, so I need to
send a modified version of patch 3 separately to Greg after these go
into "net".

Vladimir Oltean (3):
  net: dsa: stop syncing the bridge mcast_router attribute at join time
  net: dsa: mt7530: remove the .port_set_mrouter implementation
  net: dsa: don't disable multicast flooding to the CPU even without an
    IGMP querier

 drivers/net/dsa/b53/b53_common.c | 10 ----------
 drivers/net/dsa/bcm_sf2.c        |  1 -
 drivers/net/dsa/mt7530.c         | 13 -------------
 drivers/net/dsa/mv88e6xxx/chip.c | 18 ------------------
 include/net/dsa.h                |  2 --
 net/dsa/dsa_priv.h               |  2 --
 net/dsa/port.c                   | 21 ---------------------
 net/dsa/slave.c                  |  6 ------
 8 files changed, 73 deletions(-)

-- 
2.25.1

Qingfang points out that when a bridge with the default settings is
created and a port joins it:

ip link add br0 type bridge
ip link set swp0 master br0

DSA calls br_multicast_router() on the bridge to see if the br0 device
is a multicast router port, and if it is, it enables multicast flooding
to the CPU port, otherwise it disables it.

If we look through the multicast_router_show() sysfs or at the
IFLA_BR_MCAST_ROUTER netlink attribute, we see that the default mrouter
attribute for the bridge device is "1" (MDB_RTR_TYPE_TEMP_QUERY).

However, br_multicast_router() will return "0" (MDB_RTR_TYPE_DISABLED),
because an mrouter port in the MDB_RTR_TYPE_TEMP_QUERY state may not be
actually _active_ until it receives an actual IGMP query. So, the
br_multicast_router() function should really have been called
br_multicast_router_active() perhaps.

When/if an IGMP query is received, the bridge device will transition via
br_multicast_mark_router() into the active state until the
ip4_mc_router_timer expires after an multicast_querier_interval.

Of course, this does not happen if the bridge is created with an
mcast_router attribute of "2" (MDB_RTR_TYPE_PERM).

The point is that in lack of any IGMP query messages, and in the default
bridge configuration, unregistered multicast packets will not be able to
reach the CPU port through flooding, and this breaks many use cases
(most obviously, IPv6 ND, with its ICMP6 neighbor solicitation multicast
messages).

Leave the multicast flooding setting towards the CPU port down to a driver
level decision.

Fixes: 010e269f91be ("net: dsa: sync up switchdev objects and port attributes when joining the bridge")
Reported-by: DENG Qingfang <dqfext@gmail.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 net/dsa/port.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/net/dsa/port.c b/net/dsa/port.c
index 28b45b7e66df..d9ef2c2fbf88 100644
--- a/net/dsa/port.c
+++ b/net/dsa/port.c

@@ -186,10 +186,6 @@ static int dsa_port_switchdev_sync(struct dsa_port *dp,
 	if (err && err != -EOPNOTSUPP)
 		return err;
 
-	err = dsa_port_mrouter(dp->cpu_dp, br_multicast_router(br), extack);
-	if (err && err != -EOPNOTSUPP)
-		return err;
-
 	err = dsa_port_ageing_time(dp, br_get_ageing_time(br));
 	if (err && err != -EOPNOTSUPP)
 		return err;

@@ -272,12 +268,6 @@ static void dsa_port_switchdev_unsync_attrs(struct dsa_port *dp)
 
 	/* VLAN filtering is handled by dsa_switch_bridge_leave */
 
-	/* Some drivers treat the notification for having a local multicast
-	 * router by allowing multicast to be flooded to the CPU, so we should
-	 * allow this in standalone mode too.
-	 */
-	dsa_port_mrouter(dp->cpu_dp, true, NULL);
-
 	/* Ageing time may be global to the switch chip, so don't change it
 	 * here because we have no good reason (or value) to change it to.
 	 */

-- 
2.25.1

DSA's idea of optimizing out multicast flooding to the CPU port leaves
quite a few holes open, so it should be reverted.

The mt7530 driver is the only new driver which added a .port_set_mrouter
implementation after the reorg from commit a8b659e7ff75 ("net: dsa: act
as passthrough for bridge port flags"), so it needs to be reverted
separately so that the other revert commit can go a bit further down the
git history.

Fixes: 5a30833b9a16 ("net: dsa: mt7530: support MDB and bridge flag operations")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/dsa/mt7530.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
index 69f21b71614c..1f9a6b12bc7c 100644
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c

@@ -1184,18 +1184,6 @@ mt7530_port_bridge_flags(struct dsa_switch *ds, int port,
 	return 0;
 }
 
-static int
-mt7530_port_set_mrouter(struct dsa_switch *ds, int port, bool mrouter,
-			struct netlink_ext_ack *extack)
-{
-	struct mt7530_priv *priv = ds->priv;
-
-	mt7530_rmw(priv, MT7530_MFC, UNM_FFP(BIT(port)),
-		   mrouter ? UNM_FFP(BIT(port)) : 0);
-
-	return 0;
-}
-
 static int
 mt7530_port_bridge_join(struct dsa_switch *ds, int port,
 			struct net_device *bridge)

@@ -3060,7 +3048,6 @@ static const struct dsa_switch_ops mt7530_switch_ops = {
 	.port_stp_state_set	= mt7530_stp_state_set,
 	.port_pre_bridge_flags	= mt7530_port_pre_bridge_flags,
 	.port_bridge_flags	= mt7530_port_bridge_flags,
-	.port_set_mrouter	= mt7530_port_set_mrouter,
 	.port_bridge_join	= mt7530_port_bridge_join,
 	.port_bridge_leave	= mt7530_port_bridge_leave,
 	.port_fdb_add		= mt7530_port_fdb_add,

-- 
2.25.1

Commit 08cc83cc7fd8 ("net: dsa: add support for BRIDGE_MROUTER
attribute") added an option for users to turn off multicast flooding
towards the CPU if they turn off the IGMP querier on a bridge which
already has enslaved ports (echo 0 > /sys/class/net/br0/bridge/multicast_router).

And commit a8b659e7ff75 ("net: dsa: act as passthrough for bridge port flags")
simply papered over that issue, because it moved the decision to flood
the CPU with multicast (or not) from the DSA core down to individual drivers,
instead of taking a more radical position then.

The truth is that disabling multicast flooding to the CPU is simply
something we are not prepared to do now, if at all. Some reasons:

- ICMP6 neighbor solicitation messages are unregistered multicast
  packets as far as the bridge is concerned. So if we stop flooding
  multicast, the outside world cannot ping the bridge device's IPv6
  link-local address.

- There might be foreign interfaces bridged with our DSA switch ports
  (sending a packet towards the host does not necessarily equal
  termination, but maybe software forwarding). So if there is no one
  interested in that multicast traffic in the local network stack, that
  doesn't mean nobody is.

- PTP over L4 (IPv4, IPv6) is multicast, but is unregistered as far as
  the bridge is concerned. This should reach the CPU port.

- The switch driver might not do FDB partitioning. And since we don't
  even bother to do more fine-grained flood disabling (such as "disable
  flooding _from_port_N_ towards the CPU port" as opposed to "disable
  flooding _from_any_port_ towards the CPU port"), this breaks standalone
  ports, or even multiple bridges where one has an IGMP querier and one
  doesn't.

Reverting the logic makes all of the above work.

Fixes: a8b659e7ff75 ("net: dsa: act as passthrough for bridge port flags")
Fixes: 08cc83cc7fd8 ("net: dsa: add support for BRIDGE_MROUTER attribute")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/dsa/b53/b53_common.c | 10 ----------
 drivers/net/dsa/bcm_sf2.c        |  1 -
 drivers/net/dsa/mv88e6xxx/chip.c | 18 ------------------
 include/net/dsa.h                |  2 --
 net/dsa/dsa_priv.h               |  2 --
 net/dsa/port.c                   | 11 -----------
 net/dsa/slave.c                  |  6 ------
 7 files changed, 50 deletions(-)

diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index b23e3488695b..bd1417a66cbf 100644
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c

@@ -2016,15 +2016,6 @@ int b53_br_flags(struct dsa_switch *ds, int port,
 }
 EXPORT_SYMBOL(b53_br_flags);
 
-int b53_set_mrouter(struct dsa_switch *ds, int port, bool mrouter,
-		    struct netlink_ext_ack *extack)
-{
-	b53_port_set_mcast_flood(ds->priv, port, mrouter);
-
-	return 0;
-}
-EXPORT_SYMBOL(b53_set_mrouter);
-
 static bool b53_possible_cpu_port(struct dsa_switch *ds, int port)
 {
 	/* Broadcom switches will accept enabling Broadcom tags on the

@@ -2268,7 +2259,6 @@ static const struct dsa_switch_ops b53_switch_ops = {
 	.port_bridge_leave	= b53_br_leave,
 	.port_pre_bridge_flags	= b53_br_flags_pre,
 	.port_bridge_flags	= b53_br_flags,
-	.port_set_mrouter	= b53_set_mrouter,
 	.port_stp_state_set	= b53_br_set_stp_state,
 	.port_fast_age		= b53_br_fast_age,
 	.port_vlan_filtering	= b53_vlan_filtering,

diff --git a/drivers/net/dsa/bcm_sf2.c b/drivers/net/dsa/bcm_sf2.c
index 3b018fcf4412..6ce9ec1283e0 100644
--- a/drivers/net/dsa/bcm_sf2.c
+++ b/drivers/net/dsa/bcm_sf2.c

@@ -1199,7 +1199,6 @@ static const struct dsa_switch_ops bcm_sf2_ops = {
 	.port_pre_bridge_flags	= b53_br_flags_pre,
 	.port_bridge_flags	= b53_br_flags,
 	.port_stp_state_set	= b53_br_set_stp_state,
-	.port_set_mrouter	= b53_set_mrouter,
 	.port_fast_age		= b53_br_fast_age,
 	.port_vlan_filtering	= b53_vlan_filtering,
 	.port_vlan_add		= b53_vlan_add,

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 272b0535d946..111a6d5985da 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c

@@ -5781,23 +5781,6 @@ static int mv88e6xxx_port_bridge_flags(struct dsa_switch *ds, int port,
 	return err;
 }
 
-static int mv88e6xxx_port_set_mrouter(struct dsa_switch *ds, int port,
-				      bool mrouter,
-				      struct netlink_ext_ack *extack)
-{
-	struct mv88e6xxx_chip *chip = ds->priv;
-	int err;
-
-	if (!chip->info->ops->port_set_mcast_flood)
-		return -EOPNOTSUPP;
-
-	mv88e6xxx_reg_lock(chip);
-	err = chip->info->ops->port_set_mcast_flood(chip, port, mrouter);
-	mv88e6xxx_reg_unlock(chip);
-
-	return err;
-}
-
 static bool mv88e6xxx_lag_can_offload(struct dsa_switch *ds,
 				      struct net_device *lag,
 				      struct netdev_lag_upper_info *info)

@@ -6099,7 +6082,6 @@ static const struct dsa_switch_ops mv88e6xxx_switch_ops = {
 	.port_bridge_leave	= mv88e6xxx_port_bridge_leave,
 	.port_pre_bridge_flags	= mv88e6xxx_port_pre_bridge_flags,
 	.port_bridge_flags	= mv88e6xxx_port_bridge_flags,
-	.port_set_mrouter	= mv88e6xxx_port_set_mrouter,
 	.port_stp_state_set	= mv88e6xxx_port_stp_state_set,
 	.port_fast_age		= mv88e6xxx_port_fast_age,
 	.port_vlan_filtering	= mv88e6xxx_port_vlan_filtering,

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 33f40c1ec379..048d297623c9 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h

@@ -699,8 +699,6 @@ struct dsa_switch_ops {
 	int	(*port_bridge_flags)(struct dsa_switch *ds, int port,
 				     struct switchdev_brport_flags flags,
 				     struct netlink_ext_ack *extack);
-	int	(*port_set_mrouter)(struct dsa_switch *ds, int port, bool mrouter,
-				    struct netlink_ext_ack *extack);
 
 	/*
 	 * VLAN support

diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index f201c33980bf..cddf7cb0f398 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h

@@ -234,8 +234,6 @@ int dsa_port_pre_bridge_flags(const struct dsa_port *dp,
 int dsa_port_bridge_flags(const struct dsa_port *dp,
 			  struct switchdev_brport_flags flags,
 			  struct netlink_ext_ack *extack);
-int dsa_port_mrouter(struct dsa_port *dp, bool mrouter,
-		     struct netlink_ext_ack *extack);
 int dsa_port_vlan_add(struct dsa_port *dp,
 		      const struct switchdev_obj_port_vlan *vlan,
 		      struct netlink_ext_ack *extack);

diff --git a/net/dsa/port.c b/net/dsa/port.c
index d9ef2c2fbf88..23e30198a90e 100644
--- a/net/dsa/port.c
+++ b/net/dsa/port.c

@@ -597,17 +597,6 @@ int dsa_port_bridge_flags(const struct dsa_port *dp,
 	return ds->ops->port_bridge_flags(ds, dp->index, flags, extack);
 }
 
-int dsa_port_mrouter(struct dsa_port *dp, bool mrouter,
-		     struct netlink_ext_ack *extack)
-{
-	struct dsa_switch *ds = dp->ds;
-
-	if (!ds->ops->port_set_mrouter)
-		return -EOPNOTSUPP;
-
-	return ds->ops->port_set_mrouter(ds, dp->index, mrouter, extack);
-}
-
 int dsa_port_mtu_change(struct dsa_port *dp, int new_mtu,
 			bool targeted_match)
 {

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 532085da8d8f..0356ceb89a37 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c

@@ -314,12 +314,6 @@ static int dsa_slave_port_attr_set(struct net_device *dev, const void *ctx,
 
 		ret = dsa_port_bridge_flags(dp, attr->u.brport_flags, extack);
 		break;
-	case SWITCHDEV_ATTR_ID_BRIDGE_MROUTER:
-		if (!dsa_port_offloads_bridge(dp, attr->orig_dev))
-			return -EOPNOTSUPP;
-
-		ret = dsa_port_mrouter(dp->cpu_dp, attr->u.mrouter, extack);
-		break;
 	default:
 		ret = -EOPNOTSUPP;
 		break;

-- 
2.25.1

Please allow me to send a v2, I forgot to delete the function prototype
for b53_set_mrouter() and now it sticks out like a sore thumb.