Linux Ethernet Bridging - Jan 2023 - [Bridge] [PATCH v5 net-next 01/15] net: bridge: mst: Multiple Spanning Tree (MST) mode

Hi Ido,

On Mon, Jan 09, 2023 at 10:05:53AM +0200, Ido Schimmel
wrote:
> > +	if (on)
> > +		static_branch_enable(&br_mst_used);
> > +	else
> > +		static_branch_disable(&br_mst_used);
> 
> Hi,
> 
> I'm not actually using MST, but I ran into this code and was wondering
> if the static key usage is correct. The static key is global (not
> per-bridge), so what happens when two bridges have MST enabled and then
> it is disabled on one? I believe it would be disabled for both. If so,
> maybe use static_branch_inc() / static_branch_dec() instead?
Sounds about right. FWIW, br_switchdev_tx_fwd_offload does use
static_branch_inc() / static_branch_dec().

On Mon, Jan 09, 2023 at 12:02:36PM +0200, Vladimir Oltean
wrote:
> On Mon, Jan 09, 2023 at 10:05:53AM +0200, Ido Schimmel wrote:
> > > +	if (on)
> > > +		static_branch_enable(&br_mst_used);
> > > +	else
> > > +		static_branch_disable(&br_mst_used);
> > 
> > Hi,
> > 
> > I'm not actually using MST, but I ran into this code and was
wondering
> > if the static key usage is correct. The static key is global (not
> > per-bridge), so what happens when two bridges have MST enabled and
then
> > it is disabled on one? I believe it would be disabled for both. If so,
> > maybe use static_branch_inc() / static_branch_dec() instead?
> 
> Sounds about right. FWIW, br_switchdev_tx_fwd_offload does use
> static_branch_inc() / static_branch_dec().
OK, thanks for confirming. Will send a patch later this week if Tobias
won't take care of it by then. First patch will probably be [1] to make
sure we dump the correct MST state to user space. It will also make it
easier to show the problem and validate the fix.

[1]
diff --git a/net/bridge/br.c b/net/bridge/br.c
index 4f5098d33a46..f02a1ad589de 100644
--- a/net/bridge/br.c
+++ b/net/bridge/br.c
@@ -286,7 +286,7 @@ int br_boolopt_get(const struct net_bridge *br, enum
br_boolopt_id opt)
 	case BR_BOOLOPT_MCAST_VLAN_SNOOPING:
 		return br_opt_get(br, BROPT_MCAST_VLAN_SNOOPING_ENABLED);
 	case BR_BOOLOPT_MST_ENABLE:
-		return br_opt_get(br, BROPT_MST_ENABLED);
+		return br_mst_is_enabled(br);
 	default:
 		/* shouldn't be called with unsupported options */
 		WARN_ON(1);
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 75aff9bbf17e..7f0475f62d45 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -1827,7 +1827,7 @@ static inline bool br_vlan_state_allowed(u8 state, bool
learn_allow)
 /* br_mst.c */
 #ifdef CONFIG_BRIDGE_VLAN_FILTERING
 DECLARE_STATIC_KEY_FALSE(br_mst_used);
-static inline bool br_mst_is_enabled(struct net_bridge *br)
+static inline bool br_mst_is_enabled(const struct net_bridge *br)
 {
 	return static_branch_unlikely(&br_mst_used) &&
 		br_opt_get(br, BROPT_MST_ENABLED);
@@ -1845,7 +1845,7 @@ int br_mst_fill_info(struct sk_buff *skb,
 int br_mst_process(struct net_bridge_port *p, const struct nlattr *mst_attr,
 		   struct netlink_ext_ack *extack);
 #else
-static inline bool br_mst_is_enabled(struct net_bridge *br)
+static inline bool br_mst_is_enabled(const struct net_bridge *br)
 {
 	return false;
 }