netdev - [PATCH net] net: bridge: mcast: Associate the seqcount with its protecting lock.

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Message-Id: <20210928141049.593833-1-bigeasy@linutronix.de>
Date:   Tue, 28 Sep 2021 16:10:49 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     bridge@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc:     Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mike Galbraith <efault@....de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH net] net: bridge: mcast: Associate the seqcount with its protecting lock.

From: Thomas Gleixner <tglx@...utronix.de>

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: 67b746f94ff39 ("net: bridge: mcast: make sure querier port/address updates are consistent")
Reported-by: Mike Galbraith <efault@....de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Tested-by: Mike Galbraith <efault@....de>
---
 net/bridge/br_multicast.c |    6 ++----
 net/bridge/br_private.h   |    2 +-
 2 files changed, 3 insertions(+), 5 deletions(-)

--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1677,8 +1677,6 @@ static void br_multicast_update_querier(
 					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_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,
--- a/net/bridge/br_private.h
+++ b/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 */