[PATCH net] net: bonding: fix possible peer notify event loss or dup issue

[PATCH net] net: bonding: fix possible peer notify event loss or dup issue

[Tonghao Zhang]

If the send_peer_notif counter and the peer event notify are not synchronized.
It may cause problems such as the loss or dup of peer notify event.

Before this patch:
- If should_notify_peers is true and the lock for send_peer_notif-- fails, peer
  event may be sent again in next mii_monitor loop, because should_notify_peers
  is still true.
- If should_notify_peers is true and the lock for send_peer_notif-- succeeded,
  but the lock for peer event fails, the peer event will be lost.

This patch locks the RTNL for send_peer_notif, events, and commit simultaneously.

Fixes: 07a4ddec3ce9 ("bonding: add an option to specify a delay between peer notifications")
Cc: Jay Vosburgh <jv@jvosburgh.net>
Cc: Andrew Lunn <andrew+netdev@lunn.ch>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Hangbin Liu <liuhangbin@gmail.com>
Cc: Nikolay Aleksandrov <razor@blackwall.org>
Cc: Vincent Bernat <vincent@bernat.ch>
Cc: <stable@vger.kernel.org>
Signed-off-by: Tonghao Zhang <tonghao@bamaicloud.com>

---
 drivers/net/bonding/bond_main.c | 40 +++++++++++++++------------------
 1 file changed, 18 insertions(+), 22 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 5791c3e39baa..52b7ac8ddfbc 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2971,7 +2971,7 @@ static void bond_mii_monitor(struct work_struct *work)
 {
 	struct bonding *bond = container_of(work, struct bonding,
 					    mii_work.work);
-	bool should_notify_peers = false;
+	bool should_notify_peers;
 	bool commit;
 	unsigned long delay;
 	struct slave *slave;
@@ -2983,30 +2983,33 @@ static void bond_mii_monitor(struct work_struct *work)
 		goto re_arm;
 
 	rcu_read_lock();
+
 	should_notify_peers = bond_should_notify_peers(bond);
 	commit = !!bond_miimon_inspect(bond);
-	if (bond->send_peer_notif) {
-		rcu_read_unlock();
-		if (rtnl_trylock()) {
-			bond->send_peer_notif--;
-			rtnl_unlock();
-		}
-	} else {
-		rcu_read_unlock();
-	}
 
-	if (commit) {
+	rcu_read_unlock();
+
+	if (commit || bond->send_peer_notif) {
 		/* Race avoidance with bond_close cancel of workqueue */
 		if (!rtnl_trylock()) {
 			delay = 1;
-			should_notify_peers = false;
 			goto re_arm;
 		}
 
-		bond_for_each_slave(bond, slave, iter) {
-			bond_commit_link_state(slave, BOND_SLAVE_NOTIFY_LATER);
+		if (commit) {
+			bond_for_each_slave(bond, slave, iter) {
+				bond_commit_link_state(slave,
+						       BOND_SLAVE_NOTIFY_LATER);
+			}
+			bond_miimon_commit(bond);
+		}
+
+		if (bond->send_peer_notif) {
+			bond->send_peer_notif--;
+			if (should_notify_peers)
+				call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
+							 bond->dev);
 		}
-		bond_miimon_commit(bond);
 
 		rtnl_unlock();	/* might sleep, hold no other locks */
 	}
@@ -3014,13 +3017,6 @@ static void bond_mii_monitor(struct work_struct *work)
 re_arm:
 	if (bond->params.miimon)
 		queue_delayed_work(bond->wq, &bond->mii_work, delay);
-
-	if (should_notify_peers) {
-		if (!rtnl_trylock())
-			return;
-		call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, bond->dev);
-		rtnl_unlock();
-	}
 }
 
 static int bond_upper_dev_walk(struct net_device *upper,
-- 
2.34.1

Re: [PATCH net] net: bonding: fix possible peer notify event loss or dup issue

[Jay Vosburgh]

Tonghao Zhang <tonghao@bamaicloud.com> wrote:

>If the send_peer_notif counter and the peer event notify are not synchronized.
>It may cause problems such as the loss or dup of peer notify event.
>
>Before this patch:
>- If should_notify_peers is true and the lock for send_peer_notif-- fails, peer
>  event may be sent again in next mii_monitor loop, because should_notify_peers
>  is still true.
>- If should_notify_peers is true and the lock for send_peer_notif-- succeeded,
>  but the lock for peer event fails, the peer event will be lost.
>
>This patch locks the RTNL for send_peer_notif, events, and commit simultaneously.
>
>Fixes: 07a4ddec3ce9 ("bonding: add an option to specify a delay between peer notifications")
>Cc: Jay Vosburgh <jv@jvosburgh.net>
>Cc: Andrew Lunn <andrew+netdev@lunn.ch>
>Cc: Eric Dumazet <edumazet@google.com>
>Cc: Jakub Kicinski <kuba@kernel.org>
>Cc: Paolo Abeni <pabeni@redhat.com>
>Cc: Hangbin Liu <liuhangbin@gmail.com>
>Cc: Nikolay Aleksandrov <razor@blackwall.org>
>Cc: Vincent Bernat <vincent@bernat.ch>
>Cc: <stable@vger.kernel.org>
>Signed-off-by: Tonghao Zhang <tonghao@bamaicloud.com>

	I'll note that this appears to preserve the ordering of the
various events (commit, link state, notify peers).

	-J

Acked-by: Jay Vosburgh <jv@jvosburgh.net>


>---
> drivers/net/bonding/bond_main.c | 40 +++++++++++++++------------------
> 1 file changed, 18 insertions(+), 22 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index 5791c3e39baa..52b7ac8ddfbc 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -2971,7 +2971,7 @@ static void bond_mii_monitor(struct work_struct *work)
> {
> 	struct bonding *bond = container_of(work, struct bonding,
> 					    mii_work.work);
>-	bool should_notify_peers = false;
>+	bool should_notify_peers;
> 	bool commit;
> 	unsigned long delay;
> 	struct slave *slave;
>@@ -2983,30 +2983,33 @@ static void bond_mii_monitor(struct work_struct *work)
> 		goto re_arm;
> 
> 	rcu_read_lock();
>+
> 	should_notify_peers = bond_should_notify_peers(bond);
> 	commit = !!bond_miimon_inspect(bond);
>-	if (bond->send_peer_notif) {
>-		rcu_read_unlock();
>-		if (rtnl_trylock()) {
>-			bond->send_peer_notif--;
>-			rtnl_unlock();
>-		}
>-	} else {
>-		rcu_read_unlock();
>-	}
> 
>-	if (commit) {
>+	rcu_read_unlock();
>+
>+	if (commit || bond->send_peer_notif) {
> 		/* Race avoidance with bond_close cancel of workqueue */
> 		if (!rtnl_trylock()) {
> 			delay = 1;
>-			should_notify_peers = false;
> 			goto re_arm;
> 		}
> 
>-		bond_for_each_slave(bond, slave, iter) {
>-			bond_commit_link_state(slave, BOND_SLAVE_NOTIFY_LATER);
>+		if (commit) {
>+			bond_for_each_slave(bond, slave, iter) {
>+				bond_commit_link_state(slave,
>+						       BOND_SLAVE_NOTIFY_LATER);
>+			}
>+			bond_miimon_commit(bond);
>+		}
>+
>+		if (bond->send_peer_notif) {
>+			bond->send_peer_notif--;
>+			if (should_notify_peers)
>+				call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
>+							 bond->dev);
> 		}
>-		bond_miimon_commit(bond);
> 
> 		rtnl_unlock();	/* might sleep, hold no other locks */
> 	}
>@@ -3014,13 +3017,6 @@ static void bond_mii_monitor(struct work_struct *work)
> re_arm:
> 	if (bond->params.miimon)
> 		queue_delayed_work(bond->wq, &bond->mii_work, delay);
>-
>-	if (should_notify_peers) {
>-		if (!rtnl_trylock())
>-			return;
>-		call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, bond->dev);
>-		rtnl_unlock();
>-	}
> }
> 
> static int bond_upper_dev_walk(struct net_device *upper,
>-- 
>2.34.1
>

---
	-Jay Vosburgh, jv@jvosburgh.net

Re: [PATCH net] net: bonding: fix possible peer notify event loss or dup issue

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Tue, 21 Oct 2025 13:09:33 +0800 you wrote:
> If the send_peer_notif counter and the peer event notify are not synchronized.
> It may cause problems such as the loss or dup of peer notify event.
> 
> Before this patch:
> - If should_notify_peers is true and the lock for send_peer_notif-- fails, peer
>   event may be sent again in next mii_monitor loop, because should_notify_peers
>   is still true.
> - If should_notify_peers is true and the lock for send_peer_notif-- succeeded,
>   but the lock for peer event fails, the peer event will be lost.
> 
> [...]

Here is the summary with links:
  - [net] net: bonding: fix possible peer notify event loss or dup issue
    https://git.kernel.org/netdev/net/c/10843e1492e4

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html