netdev - [PATCH v2 net-next 7/7] neighbour: Convert RTM

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Message-ID: <20250418012727.57033-8-kuniyu@amazon.com>
Date: Thu, 17 Apr 2025 18:26:59 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, 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 7/7] neighbour: Convert RTM_SETNEIGHTBL to RCU.

neightbl_set() fetches neigh_tables[] and updates attributes under
write_lock_bh(&tbl->lock), so RTNL is not needed.

Let's fetch the table under RCU and drop RTNL for RTM_SETNEIGHTBL.

Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/core/neighbour.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 38732d8f0ed7..09894e559244 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2281,8 +2281,10 @@ static int neightbl_set(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	ndtmsg = nlmsg_data(nlh);
 
+	rcu_read_lock();
+
 	for (tidx = 0; tidx < NEIGH_NR_TABLES; tidx++) {
-		tbl = rcu_dereference_rtnl(neigh_tables[tidx]);
+		tbl = rcu_dereference(neigh_tables[tidx]);
 		if (!tbl)
 			continue;
 		if (ndtmsg->ndtm_family && tbl->family != ndtmsg->ndtm_family)
@@ -2293,8 +2295,10 @@ static int neightbl_set(struct sk_buff *skb, struct nlmsghdr *nlh,
 		}
 	}
 
-	if (!found)
-		return -ENOENT;
+	if (!found) {
+		err = -ENOENT;
+		goto errout_rcu;
+	}
 
 	/*
 	 * We acquire tbl->lock to be nice to the periodic timers and
@@ -2421,6 +2425,8 @@ static int neightbl_set(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 errout_tbl_lock:
 	write_unlock_bh(&tbl->lock);
+errout_rcu:
+	rcu_read_unlock();
 errout:
 	return err;
 }
@@ -3817,7 +3823,8 @@ static const struct rtnl_msg_handler neigh_rtnl_msg_handlers[] __initconst = {
 	 .flags = RTNL_FLAG_DOIT_UNLOCKED | RTNL_FLAG_DUMP_UNLOCKED},
 	{.msgtype = RTM_GETNEIGHTBL, .dumpit = neightbl_dump_info,
 	 .flags = RTNL_FLAG_DUMP_UNLOCKED},
-	{.msgtype = RTM_SETNEIGHTBL, .doit = neightbl_set},
+	{.msgtype = RTM_SETNEIGHTBL, .doit = neightbl_set,
+	 .flags = RTNL_FLAG_DOIT_UNLOCKED},
 };
 
 static int __init neigh_init(void)
-- 
2.49.0