netdev - [PATCH net-next 6/8] net: core: neighbour: Reorder netlink & internal notification

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Message-ID: <ed8cd1d500745e9707128d168d670e07586bb23a.1768225160.git.petrm@nvidia.com>
Date: Wed, 14 Jan 2026 10:54:49 +0100
From: Petr Machata <petrm@...dia.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
	<netdev@...r.kernel.org>
CC: Ido Schimmel <idosch@...dia.com>, Kuniyuki Iwashima <kuniyu@...gle.com>,
	Breno Leitao <leitao@...ian.org>, Andy Roulin <aroulin@...dia.com>,
	"Francesco Ruggeri" <fruggeri@...sta.com>, Stephen Hemminger
	<stephen@...workplumber.org>, Petr Machata <petrm@...dia.com>,
	<mlxsw@...dia.com>
Subject: [PATCH net-next 6/8] net: core: neighbour: Reorder netlink & internal notification

The netlink message needs to be send inside the critical section where the
neighbor is changed, so that it reflects the notified-upon neighbor state.
On the other hand, there is no such need in case of notifier chain: the
listeners do not assume lock, and often in fact just schedule a delayed
work to act on the neighbor later. At least one in fact also takes the
neighbor lock.

This requires that the netlink notification be done before the internal
notifier chain message is sent. That is safe to do, because the current
listeners, as well as __neigh_notify(), only read the updated neighbor
fields, and never modify them. (Apart from locking.)

Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
---
 net/core/neighbour.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index e37db91c5339..ada691690948 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1187,8 +1187,8 @@ static void neigh_timer_handler(struct timer_list *t)
 	}
 
 	if (notify) {
-		call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh);
 		neigh_notify(neigh, RTM_NEWNEIGH, 0, 0);
+		call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh);
 	}
 
 	trace_neigh_timer_handler(neigh, 0);
@@ -1523,8 +1523,8 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr,
 		neigh_update_managed_list(neigh);
 
 	if (notify) {
-		call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh);
 		neigh_notify(neigh, RTM_NEWNEIGH, 0, nlmsg_pid);
+		call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh);
 	}
 
 	trace_neigh_update_done(neigh, err);
-- 
2.51.1