[PATCH net-next v4 11/14] net: bridge: mcast: track active state, prepare for outside lock reads

["Linus Lüssing" <linus.luessing@c0d3.blue>]

We are updating ip{4,6}_active and check all variables their state relies
on while holding the bridge multicast spinlock. However we are going to
read it without this lock in a follow-up commit on fast/data path, too.

As these variables are only booleans this shouldn't be a problem,
ip{4,6}_active will be loaded and stored atomically. And those
read sides should converge eventually. But to allow tooling to verify
this use the READ_ONCE() and WRITE_ONCE macros.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
---
 net/bridge/br_multicast.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index cb78f9555db6..6faa484dede7 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1085,9 +1085,10 @@ static void br_ip4_multicast_update_active(struct net_bridge_mcast *brmctx,
 					   bool force_inactive)
 {
 	if (force_inactive)
-		brmctx->ip4_active = false;
+		WRITE_ONCE(brmctx->ip4_active, false);
 	else
-		brmctx->ip4_active = br_ip4_multicast_querier_exists(brmctx);
+		WRITE_ONCE(brmctx->ip4_active,
+			   br_ip4_multicast_querier_exists(brmctx));
 }
 
 static void br_ip6_multicast_update_active(struct net_bridge_mcast *brmctx,
@@ -1095,23 +1096,26 @@ static void br_ip6_multicast_update_active(struct net_bridge_mcast *brmctx,
 {
 #if IS_ENABLED(CONFIG_IPV6)
 	if (force_inactive)
-		brmctx->ip6_active = false;
+		WRITE_ONCE(brmctx->ip6_active, false);
 	else
-		brmctx->ip6_active = br_ip6_multicast_querier_exists(brmctx);
+		WRITE_ONCE(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)
+	int ip4_active = brmctx->ip4_active;
+	int ip6_active = brmctx->ip6_active;
+
+	if (ip4_active == ip4_active_old &&
+	    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);
+		 ip4_active_old, ip4_active, ip6_active_old, ip6_active);
 }
 
 /**
@@ -4269,7 +4273,7 @@ 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;
+	WRITE_ONCE(brmctx->ip4_active, 0);
 	seqcount_spinlock_init(&brmctx->ip4_querier.seq, &br->multicast_lock);
 	brmctx->multicast_igmp_version = 2;
 #if IS_ENABLED(CONFIG_IPV6)
@@ -4277,7 +4281,7 @@ 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;
+	WRITE_ONCE(brmctx->ip6_active, 0);
 
 	timer_setup(&brmctx->ip4_mc_router_timer, NULL, 0);
 	timer_setup(&brmctx->ip4_other_query.timer, NULL, 0);
-- 
2.53.0