net: do not acquire rtnl in fib_seq_sum()

After we made sure no fib_seq_read() handlers needs RTNL anymore,
we can remove RTNL from fib_seq_sum().

Note that after RTNL was dropped, fib_seq_sum() result was possibly
outdated anyway.

Signed-off-by: Eric Dumazet <[e-mail]>
Reviewed-by: Kuniyuki Iwashima <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/fib_notifier.h

···
 struct fib_notifier_ops {
 	int family;
 	struct list_head list;
-	unsigned int (*fib_seq_read)(struct net *net);
+	unsigned int (*fib_seq_read)(const struct net *net);
 	int (*fib_dump)(struct net *net, struct notifier_block *nb,
 			struct netlink_ext_ack *extack);
 	struct module *owner;

net/core/fib_notifier.c

···
 	struct fib_notifier_ops *ops;
 	unsigned int fib_seq = 0;
 
-	rtnl_lock();
 	rcu_read_lock();
 	list_for_each_entry_rcu(ops, &fn_net->fib_notifier_ops, list) {
 		if (!try_module_get(ops->owner))
···
 		module_put(ops->owner);
 	}
 	rcu_read_unlock();
-	rtnl_unlock();
 
 	return fib_seq;
 }

net/ipv4/fib_notifier.c

···
 	return call_fib_notifiers(net, event_type, info);
 }
 
-static unsigned int fib4_seq_read(struct net *net)
+static unsigned int fib4_seq_read(const struct net *net)
 {
 	/* Paired with WRITE_ONCE() in call_fib4_notifiers() */
 	return READ_ONCE(net->ipv4.fib_seq) + fib4_rules_seq_read(net);

net/ipv4/ipmr.c

···
 };
 #endif
 
-static unsigned int ipmr_seq_read(struct net *net)
+static unsigned int ipmr_seq_read(const struct net *net)
 {
 	return READ_ONCE(net->ipv4.ipmr_seq) + ipmr_rules_seq_read(net);
 }

net/ipv6/fib6_notifier.c

···
 	return call_fib_notifiers(net, event_type, info);
 }
 
-static unsigned int fib6_seq_read(struct net *net)
+static unsigned int fib6_seq_read(const struct net *net)
 {
 	return fib6_tables_seq_read(net) + fib6_rules_seq_read(net);
 }

net/ipv6/ip6mr.c

···
 	return NOTIFY_DONE;
 }
 
-static unsigned int ip6mr_seq_read(struct net *net)
+static unsigned int ip6mr_seq_read(const struct net *net)
 {
 	return READ_ONCE(net->ipv6.ipmr_seq) + ip6mr_rules_seq_read(net);
 }