netdev - [PATCH net-next 4/8] net: core: neighbour: Process ARP queue later

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Message-ID: <96683fb5adddb45cc79305213eae46eec8182f57.1768225160.git.petrm@nvidia.com>
Date: Wed, 14 Jan 2026 10:54:47 +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 4/8] net: core: neighbour: Process ARP queue later

ARP queue processing unlocks the neighbor lock, which can allow another
thread to asynchronously perform a neighbor update and send an out of order
notification. Therefore this needs to be done after the notification is
sent.

Move it just before the end of the critical section. Since
neigh_update_process_arp_queue() unlocks, it does not form a part of the
critical section anymore but it can benefit from the lock being taken. The
intention is to eventually do the RTNL notification before this call.

This motion crosses a call to neigh_update_is_router(), which should not
influence processing of the ARP queue.

Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
---
 net/core/neighbour.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index efbfaaba0e0b..f3290385db68 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1369,6 +1369,7 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr,
 			  struct netlink_ext_ack *extack)
 {
 	bool gc_update = false, managed_update = false;
+	bool process_arp_queue = false;
 	int update_isrouter = 0;
 	struct net_device *dev;
 	int err, notify = 0;
@@ -1504,12 +1505,17 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr,
 		neigh_suspect(neigh);
 
 	if (!(old & NUD_VALID))
-		neigh_update_process_arp_queue(neigh);
+		process_arp_queue = true;
 
 out:
 	if (update_isrouter)
 		neigh_update_is_router(neigh, flags, &notify);
+
+	if (process_arp_queue)
+		neigh_update_process_arp_queue(neigh);
+
 	write_unlock_bh(&neigh->lock);
+
 	if (((new ^ old) & NUD_PERMANENT) || gc_update)
 		neigh_update_gc_list(neigh);
 	if (managed_update)
-- 
2.51.1