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Message-ID: <253222.1762206506@vermin>
Date: Mon, 03 Nov 2025 22:48:26 +0100
From: Jay Vosburgh <jv@...sburgh.net>
To: Tonghao Zhang <tonghao@...aicloud.com>
cc: netdev@...r.kernel.org, "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>,
Jonathan Corbet <corbet@....net>,
Andrew Lunn <andrew+netdev@...n.ch>,
Nikolay Aleksandrov <razor@...ckwall.org>,
Hangbin Liu <liuhangbin@...il.com>
Subject: Re: [PATCH v2] net: bonding: use atomic instead of rtnl_mutex, to make sure peer notify updated
Tonghao Zhang <tonghao@...aicloud.com> wrote:
>Using atomic to protect the send_peer_notif instead of rtnl_mutex.
>This approach allows safe updates in both interrupt and process
>contexts, while avoiding code complexity.
>
>In lacp mode, the rtnl might be locked, preventing ad_cond_set_peer_notif()
>from acquiring the lock and updating send_peer_notif. This patch addresses
>the issue by using a atomic. Since updating send_peer_notif does not
>require high real-time performance, such atomic updates are acceptable.
>
>After coverting the rtnl lock for send_peer_notif to atomic, in bond_mii_monitor(),
>we should check the should_notify_peers (rtnllock required) instead of
>send_peer_notif. By the way, to avoid peer notify event loss, we check
>again whether to send peer notify, such as active-backup mode failover.
>
>Cc: Jay Vosburgh <jv@...sburgh.net>
>Cc: "David S. Miller" <davem@...emloft.net>
>Cc: Eric Dumazet <edumazet@...gle.com>
>Cc: Jakub Kicinski <kuba@...nel.org>
>Cc: Paolo Abeni <pabeni@...hat.com>
>Cc: Simon Horman <horms@...nel.org>
>Cc: Jonathan Corbet <corbet@....net>
>Cc: Andrew Lunn <andrew+netdev@...n.ch>
>Cc: Nikolay Aleksandrov <razor@...ckwall.org>
>Cc: Hangbin Liu <liuhangbin@...il.com>
>Suggested-by: Jay Vosburgh <jv@...sburgh.net>
>Signed-off-by: Tonghao Zhang <tonghao@...aicloud.com>
>---
>v2:
>- refine the codes
>- check bond_should_notify_peers again in bond_mii_monitor(), to avoid
> event loss.
>- v1 https://patchwork.kernel.org/project/netdevbpf/patch/20251026095614.48833-1-tonghao@bamaicloud.com/
>---
> drivers/net/bonding/bond_3ad.c | 7 ++---
> drivers/net/bonding/bond_main.c | 46 ++++++++++++++++-----------------
> include/net/bonding.h | 9 ++++++-
> 3 files changed, 32 insertions(+), 30 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
>index 49717b7b82a2..05c573e45450 100644
>--- a/drivers/net/bonding/bond_3ad.c
>+++ b/drivers/net/bonding/bond_3ad.c
>@@ -999,11 +999,8 @@ static void ad_cond_set_peer_notif(struct port *port)
> {
> struct bonding *bond = port->slave->bond;
>
>- if (bond->params.broadcast_neighbor && rtnl_trylock()) {
>- bond->send_peer_notif = bond->params.num_peer_notif *
>- max(1, bond->params.peer_notif_delay);
>- rtnl_unlock();
>- }
>+ if (bond->params.broadcast_neighbor)
>+ bond_peer_notify_reset(bond);
> }
>
> /**
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index 8e592f37c28b..ae90221838d4 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -1167,10 +1167,11 @@ static bool bond_should_notify_peers(struct bonding *bond)
> {
> struct bond_up_slave *usable;
> struct slave *slave = NULL;
>+ int send_peer_notif;
>
>- if (!bond->send_peer_notif ||
>- bond->send_peer_notif %
>- max(1, bond->params.peer_notif_delay) != 0 ||
>+ send_peer_notif = atomic_read(&bond->send_peer_notif);
>+ if (!send_peer_notif ||
>+ send_peer_notif % max(1, bond->params.peer_notif_delay) != 0 ||
> !netif_carrier_ok(bond->dev))
> return false;
>
>@@ -1270,8 +1271,6 @@ void bond_change_active_slave(struct bonding *bond, struct slave *new_active)
> BOND_SLAVE_NOTIFY_NOW);
>
> if (new_active) {
>- bool should_notify_peers = false;
>-
> bond_set_slave_active_flags(new_active,
> BOND_SLAVE_NOTIFY_NOW);
>
>@@ -1280,19 +1279,17 @@ void bond_change_active_slave(struct bonding *bond, struct slave *new_active)
> old_active);
>
> if (netif_running(bond->dev)) {
>- bond->send_peer_notif =
>- bond->params.num_peer_notif *
>- max(1, bond->params.peer_notif_delay);
>- should_notify_peers =
>- bond_should_notify_peers(bond);
>+ bond_peer_notify_reset(bond);
>+
>+ if (bond_should_notify_peers(bond)) {
>+ atomic_dec(&bond->send_peer_notif);
>+ call_netdevice_notifiers(
>+ NETDEV_NOTIFY_PEERS,
>+ bond->dev);
>+ }
> }
>
> call_netdevice_notifiers(NETDEV_BONDING_FAILOVER, bond->dev);
>- if (should_notify_peers) {
>- bond->send_peer_notif--;
>- call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
>- bond->dev);
>- }
> }
> }
>
>@@ -2801,7 +2798,7 @@ static void bond_mii_monitor(struct work_struct *work)
>
> rcu_read_unlock();
>
>- if (commit || bond->send_peer_notif) {
>+ if (commit || should_notify_peers) {
> /* Race avoidance with bond_close cancel of workqueue */
> if (!rtnl_trylock()) {
> delay = 1;
>@@ -2816,16 +2813,15 @@ static void bond_mii_monitor(struct work_struct *work)
> 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);
>- }
>+ /* check again to avoid send_peer_notif has been changed. */
>+ if (bond_should_notify_peers(bond))
>+ call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, bond->dev);
Is the risk here that user space may have set send_peer_notify
to zero?
>
> rtnl_unlock(); /* might sleep, hold no other locks */
> }
>
>+ atomic_dec_if_positive(&bond->send_peer_notif);
>+
Also, it's a bit subtle, but I think this has to be outside of
the if block, or peer_notif_delay may be unreliable. I'm not sure it
needs a comment, but could you confirm that's why this line is where it
is?
-J
> re_arm:
> if (bond->params.miimon)
> queue_delayed_work(bond->wq, &bond->mii_work, delay);
>@@ -3773,7 +3769,7 @@ static void bond_activebackup_arp_mon(struct bonding *bond)
> return;
>
> if (should_notify_peers) {
>- bond->send_peer_notif--;
>+ atomic_dec(&bond->send_peer_notif);
> call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
> bond->dev);
> }
>@@ -4267,6 +4263,8 @@ static int bond_open(struct net_device *bond_dev)
> queue_delayed_work(bond->wq, &bond->alb_work, 0);
> }
>
>+ atomic_set(&bond->send_peer_notif, 0);
>+
> if (bond->params.miimon) /* link check interval, in milliseconds. */
> queue_delayed_work(bond->wq, &bond->mii_work, 0);
>
>@@ -4300,7 +4298,7 @@ static int bond_close(struct net_device *bond_dev)
> struct slave *slave;
>
> bond_work_cancel_all(bond);
>- bond->send_peer_notif = 0;
>+ atomic_set(&bond->send_peer_notif, 0);
> if (bond_is_lb(bond))
> bond_alb_deinitialize(bond);
> bond->recv_probe = NULL;
>diff --git a/include/net/bonding.h b/include/net/bonding.h
>index 49edc7da0586..afdfcb5bfaf0 100644
>--- a/include/net/bonding.h
>+++ b/include/net/bonding.h
>@@ -236,7 +236,7 @@ struct bonding {
> */
> spinlock_t mode_lock;
> spinlock_t stats_lock;
>- u32 send_peer_notif;
>+ atomic_t send_peer_notif;
> u8 igmp_retrans;
> #ifdef CONFIG_PROC_FS
> struct proc_dir_entry *proc_entry;
>@@ -814,4 +814,11 @@ static inline netdev_tx_t bond_tx_drop(struct net_device *dev, struct sk_buff *s
> return NET_XMIT_DROP;
> }
>
>+static inline void bond_peer_notify_reset(struct bonding *bond)
>+{
>+ atomic_set(&bond->send_peer_notif,
>+ bond->params.num_peer_notif *
>+ max(1, bond->params.peer_notif_delay));
>+}
>+
> #endif /* _NET_BONDING_H */
>--
>2.34.1
>
---
-Jay Vosburgh, jv@...sburgh.net
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