net: bridge: mcast: Associate the seqcount with its protecting lock.

The sequence count bridge_mcast_querier::seq is protected by
net_bridge::multicast_lock but seqcount_init() does not associate the
seqcount with the lock. This leads to a warning on PREEMPT_RT because
preemption is still enabled.

Let seqcount_init() associate the seqcount with lock that protects the
write section. Remove lockdep_assert_held_once() because lockdep already checks
whether the associated lock is held.

Fixes: 67b746f9 ("net: bridge: mcast: make sure querier port/address updates are consistent")
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Mike Galbraith <efault@gmx.de>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Link: https://lore.kernel.org/r/20210928141049.593833-1-bigeasy@linutronix.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/bridge/br_multicast.c

@@ -1677,8 +1677,6 @@ static void br_multicast_update_querier(struct net_bridge_mcast *brmctx,
 					int ifindex,
 					struct br_ip *saddr)
 {
-	lockdep_assert_held_once(&brmctx->br->multicast_lock);
-
 	write_seqcount_begin(&querier->seq);
 	querier->port_ifidx = ifindex;
 	memcpy(&querier->addr, saddr, sizeof(*saddr));
@@ -3867,13 +3865,13 @@ void br_multicast_ctx_init(struct net_bridge *br,
 
 	brmctx->ip4_other_query.delay_time = 0;
 	brmctx->ip4_querier.port_ifidx = 0;
-	seqcount_init(&brmctx->ip4_querier.seq);
+	seqcount_spinlock_init(&brmctx->ip4_querier.seq, &br->multicast_lock);
 	brmctx->multicast_igmp_version = 2;
 #if IS_ENABLED(CONFIG_IPV6)
 	brmctx->multicast_mld_version = 1;
 	brmctx->ip6_other_query.delay_time = 0;
 	brmctx->ip6_querier.port_ifidx = 0;
-	seqcount_init(&brmctx->ip6_querier.seq);
+	seqcount_spinlock_init(&brmctx->ip6_querier.seq, &br->multicast_lock);
 #endif
 
 	timer_setup(&brmctx->ip4_mc_router_timer,

net/bridge/br_private.h

@@ -82,7 +82,7 @@ struct bridge_mcast_other_query {
 struct bridge_mcast_querier {
 	struct br_ip addr;
 	int port_ifidx;
-	seqcount_t seq;
+	seqcount_spinlock_t seq;
 };
 
 /* IGMP/MLD statistics */