[PATCH net-next v4 04/14] net: bridge: mcast: track active state, IGMP/MLD querier appearance

Linus Lüssing
2026-03-07T04:46:14Z

This is the first step to track in dedicated, per protocol family
variables if we can actively and safely use multicast snooping.
To later use these in the fast/data path instead of performing
all these checks for every packet and to later notify DSA/switchdev
about this state.

This toggles these new variables to true after a Maximum Response Delay
(default: 10 seconds) if a new IGMP or MLD querier has appeared. This
can be triggered either through receiving an IGMP/MLD query from another
host or by a user enabling our own IGMP/MLD querier.

This is the first of several requirements, similar to what
br_multicast_querier_exists() already checks so far, to be able to
reliably receive IGMP/MLD reports, which in turn are needed to build
a complete multicast database.

No functional change for the fast/data path yet.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
---
net/bridge/br_multicast.c | 116 +++++++++++++++++++++++++++++++++++++-
net/bridge/br_private.h | 2 +
2 files changed, 115 insertions(+), 3 deletions(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index cfe8d42f0214..9c22ec63fc6b 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1067,6 +1067,84 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm
return skb;
}

+static bool br_ip4_multicast_querier_exists(struct net_bridge_mcast *brmctx)
+{
+ return __br_multicast_querier_exists(brmctx, &brmctx->ip4_other_query,
+ false);
+}
+
+#if IS_ENABLED(CONFIG_IPV6)
+static bool br_ip6_multicast_querier_exists(struct net_bridge_mcast *brmctx)
+{
+ return __br_multicast_querier_exists(brmctx, &brmctx->ip6_other_query,
+ true);
+}
+#endif
+
+static void br_ip4_multicast_update_active(struct net_bridge_mcast *brmctx,
+ bool force_inactive)
+{
+ if (force_inactive)
+ brmctx->ip4_active = false;
+ else
+ brmctx->ip4_active = br_ip4_multicast_querier_exists(brmctx);
+}
+
+static void br_ip6_multicast_update_active(struct net_bridge_mcast *brmctx,
+ bool force_inactive)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+ if (force_inactive)
+ brmctx->ip6_active = false;
+ else
+ brmctx->ip6_active = br_ip6_multicast_querier_exists(brmctx);
+#endif
+}
+
+static void br_multicast_notify_active(struct net_bridge_mcast *brmctx,
+ bool ip4_active_old, bool ip6_active_old)
+{
+ if (brmctx->ip4_active == ip4_active_old &&
+ brmctx->ip6_active == ip6_active_old)
+ return;
+
+ br_debug(brmctx->br, "mc_active changed, vid: %i: v4: %i->%i, v6: %i->%i\n",
+ brmctx->vlan ? brmctx->vlan->vid : -1,
+ ip4_active_old, brmctx->ip4_active,
+ ip6_active_old, brmctx->ip6_active);
+}
+
+/**
+ * br_multicast_update_active() - update mcast active state
+ * @brmctx: the bridge multicast context to check
+ *
+ * This (potentially) updates the IPv4/IPv6 multicast active state. And by
+ * that enables or disables snooping of multicast payload traffic in fast
+ * path.
+ *
+ * The multicast active state is set, per protocol family, if:
+ *
+ * - an IGMP/MLD querier is present
+ *
+ * And is unset otherwise.
+ *
+ * This function should be called by anything that changes one of the
+ * above prerequisites.
+ */
+static void br_multicast_update_active(struct net_bridge_mcast *brmctx)
+{
+ bool ip4_active_old = brmctx->ip4_active;
+ bool ip6_active_old = brmctx->ip6_active;
+ bool force_inactive = false;
+
+ lockdep_assert_held_once(&brmctx->br->multicast_lock);
+
+ br_ip4_multicast_update_active(brmctx, force_inactive);
+ br_ip6_multicast_update_active(brmctx, force_inactive);
+
+ br_multicast_notify_active(brmctx, ip4_active_old, ip6_active_old);
+}
+
#if IS_ENABLED(CONFIG_IPV6)
static struct sk_buff *br_ip6_multicast_alloc_query(struct net_bridge_mcast *brmctx,
struct net_bridge_mcast_port *pmctx,
@@ -1770,10 +1848,40 @@ static void br_ip6_multicast_querier_expired(struct timer_list *t)
}
#endif

-static void br_multicast_query_delay_expired(struct timer_list *t)
+static void br_ip4_multicast_query_delay_expired(struct timer_list *t)
{
+ struct net_bridge_mcast *brmctx;
+
+ brmctx = timer_container_of(brmctx, t, ip4_other_query.delay_timer);
+
+ spin_lock(&brmctx->br->multicast_lock);
+ if (!br_multicast_is_stopping(brmctx->br, t))
+ /* an own or other IGMP querier appeared some seconds ago and
+ * all reports should have arrived by now, maybe set multicast
+ * state to active
+ */
+ br_multicast_update_active(brmctx);
+ spin_unlock(&brmctx->br->multicast_lock);
}

+#if IS_ENABLED(CONFIG_IPV6)
+static void br_ip6_multicast_query_delay_expired(struct timer_list *t)
+{
+ struct net_bridge_mcast *brmctx;
+
+ brmctx = timer_container_of(brmctx, t, ip6_other_query.delay_timer);
+
+ spin_lock(&brmctx->br->multicast_lock);
+ if (!br_multicast_is_stopping(brmctx->br, t))
+ /* an own or other MLD querier appeared some seconds ago and
+ * all reports should have arrived by now, maybe set multicast
+ * state to active
+ */
+ br_multicast_update_active(brmctx);
+ spin_unlock(&brmctx->br->multicast_lock);
+}
+#endif
+
static void br_multicast_select_own_querier(struct net_bridge_mcast *brmctx,
struct br_ip *ip,
struct sk_buff *skb)
@@ -4115,6 +4223,7 @@ void br_multicast_ctx_init(struct net_bridge *br,
brmctx->multicast_membership_interval = 260 * HZ;

brmctx->ip4_querier.port_ifidx = 0;
+ brmctx->ip4_active = 0;
seqcount_spinlock_init(&brmctx->ip4_querier.seq, &br->multicast_lock);
brmctx->multicast_igmp_version = 2;
#if IS_ENABLED(CONFIG_IPV6)
@@ -4122,6 +4231,7 @@ void br_multicast_ctx_init(struct net_bridge *br,
brmctx->ip6_querier.port_ifidx = 0;
seqcount_spinlock_init(&brmctx->ip6_querier.seq, &br->multicast_lock);
#endif
+ brmctx->ip6_active = 0;

timer_setup(&brmctx->ip4_mc_router_timer, NULL, 0);
timer_setup(&brmctx->ip4_other_query.timer, NULL, 0);
@@ -4245,7 +4355,7 @@ void br_multicast_reset_timer_cbs(struct net_bridge_mcast *brmctx)
brmctx->ip4_other_query.timer.function =
br_ip4_multicast_querier_expired;
brmctx->ip4_other_query.delay_timer.function =
- br_multicast_query_delay_expired;
+ br_ip4_multicast_query_delay_expired;
brmctx->ip4_own_query.timer.function =
br_ip4_multicast_query_expired;
#if IS_ENABLED(CONFIG_IPV6)
@@ -4254,7 +4364,7 @@ void br_multicast_reset_timer_cbs(struct net_bridge_mcast *brmctx)
brmctx->ip6_other_query.timer.function =
br_ip6_multicast_querier_expired;
brmctx->ip6_other_query.delay_timer.function =
- br_multicast_query_delay_expired;
+ br_ip6_multicast_query_delay_expired;
brmctx->ip6_own_query.timer.function =
br_ip6_multicast_query_expired;
#endif
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index af206a41555c..8d1c869eb522 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -160,6 +160,7 @@ struct net_bridge_mcast {
struct bridge_mcast_other_query ip4_other_query;
struct bridge_mcast_own_query ip4_own_query;
struct bridge_mcast_querier ip4_querier;
+ bool ip4_active;
#if IS_ENABLED(CONFIG_IPV6)
struct hlist_head ip6_mc_router_list;
struct timer_list ip6_mc_router_timer;
@@ -167,6 +168,7 @@ struct net_bridge_mcast {
struct bridge_mcast_own_query ip6_own_query;
struct bridge_mcast_querier ip6_querier;
#endif /* IS_ENABLED(CONFIG_IPV6) */
+ bool ip6_active;
#endif /* CONFIG_BRIDGE_IGMP_SNOOPING */
};

--
2.53.0