From: Yong Wang yongwang@nvidia.com
[ Upstream commit 4b30ae9adb047dd0a7982975ec3933c529537026 ]
When a bridge port STP state is changed from BLOCKING/DISABLED to FORWARDING, the port's igmp query timer will NOT re-arm itself if the bridge has been configured as per-VLAN multicast snooping.
Solve this by choosing the correct multicast context(s) to enable/disable port multicast based on whether per-VLAN multicast snooping is enabled or not, i.e. using per-{port, VLAN} context in case of per-VLAN multicast snooping by re-implementing br_multicast_enable_port() and br_multicast_disable_port() functions.
Before the patch, the IGMP query does not happen in the last step of the following test sequence, i.e. no growth for tx counter: # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1 mcast_querier 1 mcast_stats_enabled 1 # bridge vlan global set vid 1 dev br1 mcast_snooping 1 mcast_querier 1 mcast_query_interval 100 mcast_startup_query_count 0 # ip link add name swp1 up master br1 type dummy # bridge link set dev swp1 state 0 # ip -j -p stats show dev swp1 group xstats_slave subgroup bridge suite mcast | jq '.[]["multicast"]["igmp_queries"]["tx_v2"]' 1 # sleep 1 # ip -j -p stats show dev swp1 group xstats_slave subgroup bridge suite mcast | jq '.[]["multicast"]["igmp_queries"]["tx_v2"]' 1 # bridge link set dev swp1 state 3 # sleep 2 # ip -j -p stats show dev swp1 group xstats_slave subgroup bridge suite mcast | jq '.[]["multicast"]["igmp_queries"]["tx_v2"]' 1
After the patch, the IGMP query happens in the last step of the test: # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1 mcast_querier 1 mcast_stats_enabled 1 # bridge vlan global set vid 1 dev br1 mcast_snooping 1 mcast_querier 1 mcast_query_interval 100 mcast_startup_query_count 0 # ip link add name swp1 up master br1 type dummy # bridge link set dev swp1 state 0 # ip -j -p stats show dev swp1 group xstats_slave subgroup bridge suite mcast | jq '.[]["multicast"]["igmp_queries"]["tx_v2"]' 1 # sleep 1 # ip -j -p stats show dev swp1 group xstats_slave subgroup bridge suite mcast | jq '.[]["multicast"]["igmp_queries"]["tx_v2"]' 1 # bridge link set dev swp1 state 3 # sleep 2 # ip -j -p stats show dev swp1 group xstats_slave subgroup bridge suite mcast | jq '.[]["multicast"]["igmp_queries"]["tx_v2"]' 3
Signed-off-by: Yong Wang yongwang@nvidia.com Reviewed-by: Andy Roulin aroulin@nvidia.com Reviewed-by: Ido Schimmel idosch@nvidia.com Signed-off-by: Petr Machata petrm@nvidia.com Acked-by: Nikolay Aleksandrov razor@blackwall.org Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my comprehensive analysis, here's my assessment: **YES** ## Analysis Summary This commit should be backported to stable kernel trees. Here's my detailed reasoning: ### **What the Bug Fixes** The commit fixes a critical bug where **IGMP query timers fail to re-arm** when a bridge port transitions from BLOCKING/DISABLED to FORWARDING state in **per-VLAN multicast snooping** configurations. ### **Technical Problem** 1. **Context**: When `BROPT_MCAST_VLAN_SNOOPING_ENABLED` is active, each VLAN has its own multicast context (`port_mcast_ctx`) with separate query timers 2. **Bug**: The old implementation in `br_multicast_enable_port()` and `br_multicast_disable_port()` only operated on the port's main multicast context (`port->multicast_ctx`) 3. **Impact**: Per-VLAN multicast contexts were never properly enabled/disabled during STP state transitions 4. **Result**: IGMP/MLD query timers for VLANs remain permanently disabled, causing multicast flooding instead of proper snooping ### **Evidence from Commit** The commit message provides clear **before/after test results**: - **Before**: IGMP query count stays at 1 (timer not re-arming) - **After**: IGMP query count increases to 3 (timer properly re-arming) This demonstrates the fix works and solves a real, testable problem. ### **Code Analysis** The fix **re-implements** `br_multicast_enable_port()` and `br_multicast_disable_port()` to: 1. **Check VLAN snooping status**: If `BROPT_MCAST_VLAN_SNOOPING_ENABLED` is set 2. **Iterate through VLANs**: Process each VLAN's multicast context individually 3. **Proper state handling**: Only enable contexts for VLANs in LEARNING/FORWARDING states 4. **Fallback behavior**: Use old behavior when VLAN snooping is disabled ### **Backporting Criteria Met** ✅ **Bug Fix**: Fixes functional regression in multicast snooping ✅ **Self-contained**: Changes isolated to bridge multicast code ✅ **No API changes**: Pure internal refactoring with same public interface ✅ **Production Impact**: Affects real-world VLAN multicast deployments ✅ **Well-tested**: Includes specific test case demonstrating the fix ✅ **Minimal Risk**: Well-reviewed code from experienced maintainers (Nvidia networking team) ### **Stability Impact** - **Risk Level**: Low - internal refactoring with clear improvement - **Regression Potential**: Very low - maintains backward compatibility - **User Impact**: High - fixes broken multicast functionality in VLAN scenarios This is exactly the type of targeted bug fix that stable trees are designed to include: it fixes a clear functional regression affecting production deployments while carrying minimal risk of introducing new issues.
net/bridge/br_multicast.c | 77 +++++++++++++++++++++++++++++++++++---- 1 file changed, 69 insertions(+), 8 deletions(-)
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index 5972821ce1950..e28c9db0c4db2 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -1931,12 +1931,17 @@ static void __br_multicast_enable_port_ctx(struct net_bridge_mcast_port *pmctx) } }
-void br_multicast_enable_port(struct net_bridge_port *port) +static void br_multicast_enable_port_ctx(struct net_bridge_mcast_port *pmctx) { - struct net_bridge *br = port->br; + struct net_bridge *br = pmctx->port->br;
spin_lock_bh(&br->multicast_lock); - __br_multicast_enable_port_ctx(&port->multicast_ctx); + if (br_multicast_port_ctx_is_vlan(pmctx) && + !(pmctx->vlan->priv_flags & BR_VLFLAG_MCAST_ENABLED)) { + spin_unlock_bh(&br->multicast_lock); + return; + } + __br_multicast_enable_port_ctx(pmctx); spin_unlock_bh(&br->multicast_lock); }
@@ -1963,11 +1968,67 @@ static void __br_multicast_disable_port_ctx(struct net_bridge_mcast_port *pmctx) br_multicast_rport_del_notify(pmctx, del); }
+static void br_multicast_disable_port_ctx(struct net_bridge_mcast_port *pmctx) +{ + struct net_bridge *br = pmctx->port->br; + + spin_lock_bh(&br->multicast_lock); + if (br_multicast_port_ctx_is_vlan(pmctx) && + !(pmctx->vlan->priv_flags & BR_VLFLAG_MCAST_ENABLED)) { + spin_unlock_bh(&br->multicast_lock); + return; + } + + __br_multicast_disable_port_ctx(pmctx); + spin_unlock_bh(&br->multicast_lock); +} + +static void br_multicast_toggle_port(struct net_bridge_port *port, bool on) +{ +#if IS_ENABLED(CONFIG_BRIDGE_VLAN_FILTERING) + if (br_opt_get(port->br, BROPT_MCAST_VLAN_SNOOPING_ENABLED)) { + struct net_bridge_vlan_group *vg; + struct net_bridge_vlan *vlan; + + rcu_read_lock(); + vg = nbp_vlan_group_rcu(port); + if (!vg) { + rcu_read_unlock(); + return; + } + + /* iterate each vlan, toggle vlan multicast context */ + list_for_each_entry_rcu(vlan, &vg->vlan_list, vlist) { + struct net_bridge_mcast_port *pmctx = + &vlan->port_mcast_ctx; + u8 state = br_vlan_get_state(vlan); + /* enable vlan multicast context when state is + * LEARNING or FORWARDING + */ + if (on && br_vlan_state_allowed(state, true)) + br_multicast_enable_port_ctx(pmctx); + else + br_multicast_disable_port_ctx(pmctx); + } + rcu_read_unlock(); + return; + } +#endif + /* toggle port multicast context when vlan snooping is disabled */ + if (on) + br_multicast_enable_port_ctx(&port->multicast_ctx); + else + br_multicast_disable_port_ctx(&port->multicast_ctx); +} + +void br_multicast_enable_port(struct net_bridge_port *port) +{ + br_multicast_toggle_port(port, true); +} + void br_multicast_disable_port(struct net_bridge_port *port) { - spin_lock_bh(&port->br->multicast_lock); - __br_multicast_disable_port_ctx(&port->multicast_ctx); - spin_unlock_bh(&port->br->multicast_lock); + br_multicast_toggle_port(port, false); }
static int __grp_src_delete_marked(struct net_bridge_port_group *pg) @@ -4156,9 +4217,9 @@ int br_multicast_toggle_vlan_snooping(struct net_bridge *br, bool on, __br_multicast_open(&br->multicast_ctx); list_for_each_entry(p, &br->port_list, list) { if (on) - br_multicast_disable_port(p); + br_multicast_disable_port_ctx(&p->multicast_ctx); else - br_multicast_enable_port(p); + br_multicast_enable_port_ctx(&p->multicast_ctx); }
list_for_each_entry(vlan, &vg->vlan_list, vlist)