netdev - [PATCH v2 net-next 14/14] ipv6: Get rid of RTNL for SIOCADDRT and RTM

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Message-ID: <20250409011243.26195-15-kuniyu@amazon.com>
Date: Tue, 8 Apr 2025 18:12:22 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "Paolo
 Abeni" <pabeni@...hat.com>
CC: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>,
	Kuniyuki Iwashima <kuni1840@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH v2 net-next 14/14] ipv6: Get rid of RTNL for SIOCADDRT and RTM_NEWROUTE.

Now we are ready to remove RTNL from SIOCADDRT and RTM_NEWROUTE.

The remaining things to do are

  1. pass false to lwtunnel_valid_encap_type_attr()
  2. use rcu_dereference_rtnl() in fib6_check_nexthop()
  3. place rcu_read_lock() before ip6_route_info_create_nh().

Let's complete the RTNL-free conversion.

When each CPU-X adds 100000 routes on table-X in a batch
concurrently on c7a.metal-48xl EC2 instance with 192 CPUs,

without this series:

  $ sudo ./route_test.sh
  start adding routes
  added 19200000 routes (100000 routes * 192 tables).
  total routes: 19200006
  Time elapsed: 191577 milliseconds.

with series:

  $ sudo ./route_test.sh
  start adding routes
  added 19200000 routes (100000 routes * 192 tables).
  total routes: 19200006
  Time elapsed: 62854 milliseconds.

I changed the number of routes in each table (1000 ~ 100000)
and consistently saw it finish 3x faster with this series.

Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/ipv4/nexthop.c |  4 ++--
 net/ipv6/route.c   | 18 ++++++++++++------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
index 5e47166512e2..329f33a2be51 100644
--- a/net/ipv4/nexthop.c
+++ b/net/ipv4/nexthop.c
@@ -1556,12 +1556,12 @@ int fib6_check_nexthop(struct nexthop *nh, struct fib6_config *cfg,
 	if (nh->is_group) {
 		struct nh_group *nhg;
 
-		nhg = rtnl_dereference(nh->nh_grp);
+		nhg = rcu_dereference_rtnl(nh->nh_grp);
 		if (nhg->has_v4)
 			goto no_v4_nh;
 		is_fdb_nh = nhg->fdb_nh;
 	} else {
-		nhi = rtnl_dereference(nh->nh_info);
+		nhi = rcu_dereference_rtnl(nh->nh_info);
 		if (nhi->family == AF_INET)
 			goto no_v4_nh;
 		is_fdb_nh = nhi->fdb_nh;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 26a0be592632..d6052a7ae12b 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3902,12 +3902,16 @@ int ip6_route_add(struct fib6_config *cfg, gfp_t gfp_flags,
 	if (IS_ERR(rt))
 		return PTR_ERR(rt);
 
+	rcu_read_lock();
+
 	err = ip6_route_info_create_nh(rt, cfg, extack);
 	if (err)
-		return err;
+		goto unlock;
 
 	err = __ip6_ins_rt(rt, &cfg->fc_nlinfo, extack);
 	fib6_info_release(rt);
+unlock:
+	rcu_read_unlock();
 
 	return err;
 }
@@ -4528,12 +4532,10 @@ int ipv6_route_ioctl(struct net *net, unsigned int cmd, struct in6_rtmsg *rtmsg)
 
 	switch (cmd) {
 	case SIOCADDRT:
-		rtnl_lock();
 		/* Only do the default setting of fc_metric in route adding */
 		if (cfg.fc_metric == 0)
 			cfg.fc_metric = IP6_RT_PRIO_USER;
 		err = ip6_route_add(&cfg, GFP_KERNEL, NULL);
-		rtnl_unlock();
 		break;
 	case SIOCDELRT:
 		err = ip6_route_del(&cfg, NULL);
@@ -5112,7 +5114,7 @@ static int rtm_to_fib6_multipath_config(struct fib6_config *cfg,
 	} while (rtnh_ok(rtnh, remaining));
 
 	return lwtunnel_valid_encap_type_attr(cfg->fc_mp, cfg->fc_mp_len,
-					      extack, newroute);
+					      extack, false);
 }
 
 static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
@@ -5250,7 +5252,7 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
 		cfg->fc_encap_type = nla_get_u16(tb[RTA_ENCAP_TYPE]);
 
 		err = lwtunnel_valid_encap_type(cfg->fc_encap_type,
-						extack, newroute);
+						extack, false);
 		if (err < 0)
 			goto errout;
 	}
@@ -5517,6 +5519,8 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
 	if (err)
 		return err;
 
+	rcu_read_lock();
+
 	err = ip6_route_mpath_info_create_nh(&rt6_nh_list, extack);
 	if (err)
 		goto cleanup;
@@ -5608,6 +5612,8 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
 	}
 
 cleanup:
+	rcu_read_unlock();
+
 	list_for_each_entry_safe(nh, nh_safe, &rt6_nh_list, next) {
 		fib6_info_release(nh->fib6_info);
 		list_del(&nh->next);
@@ -6890,7 +6896,7 @@ static void bpf_iter_unregister(void)
 
 static const struct rtnl_msg_handler ip6_route_rtnl_msg_handlers[] __initconst_or_module = {
 	{.owner = THIS_MODULE, .protocol = PF_INET6, .msgtype = RTM_NEWROUTE,
-	 .doit = inet6_rtm_newroute},
+	 .doit = inet6_rtm_newroute, .flags = RTNL_FLAG_DOIT_UNLOCKED},
 	{.owner = THIS_MODULE, .protocol = PF_INET6, .msgtype = RTM_DELROUTE,
 	 .doit = inet6_rtm_delroute, .flags = RTNL_FLAG_DOIT_UNLOCKED},
 	{.owner = THIS_MODULE, .protocol = PF_INET6, .msgtype = RTM_GETROUTE,
-- 
2.49.0