Re: [PATCH RESEND net-next v4 1/4] net: bonding: use workqueue to make sure peer notify updated in lacp mode

[Hangbin Liu <liuhangbin@gmail.com>]

On Mon, Jan 12, 2026 at 10:40:48AM +0800, Tonghao Zhang wrote:
> The rtnl lock 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 workqueue. Since updating send_peer_notif does
> not require high real-time performance, such delayed updates are entirely
> acceptable.
> 
> In fact, checking this value and using it in multiple places, all operations
> are protected at the same time by rtnl lock, such as
> - read send_peer_notif
> - send_peer_notif--
> - bond_should_notify_peers
> 
> By the way, rtnl lock is still required, when accessing bond.params.* for
> updating send_peer_notif. In lacp mode, resetting send_peer_notif in
> workqueue is safe, simple and effective way.
> 
> Cc: Jay Vosburgh <jv@jvosburgh.net>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: Simon Horman <horms@kernel.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Andrew Lunn <andrew+netdev@lunn.ch>
> Cc: Nikolay Aleksandrov <razor@blackwall.org>
> Cc: Hangbin Liu <liuhangbin@gmail.com>
> Cc: Jason Xing <kerneljasonxing@gmail.com>
> Suggested-by: Hangbin Liu <liuhangbin@gmail.com>
> Signed-off-by: Tonghao Zhang <tonghao@bamaicloud.com>
> ---
> v4:
> - keep the netdevice notifier order.
> v2/3:
> - no change
> v1:
> - This patch is actually version v3, https://patchwork.kernel.org/project/netdevbpf/patch/20251118090305.35558-1-tonghao@bamaicloud.com/
> - add a comment why we use the trylock.
> - add this patch to series
> ---
>  drivers/net/bonding/bond_3ad.c  |  7 ++--
>  drivers/net/bonding/bond_main.c | 57 +++++++++++++++++++++++++--------
>  include/net/bonding.h           |  2 ++
>  3 files changed, 48 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
> index 1a8de2bf8655..01ae0269a138 100644
> --- a/drivers/net/bonding/bond_3ad.c
> +++ b/drivers/net/bonding/bond_3ad.c
> @@ -1008,11 +1008,8 @@ 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_work_rearm(bond, 0);
>  }
>  
>  /**
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 3d56339a8a10..edf6dac8a98f 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -1195,6 +1195,35 @@ static bool bond_should_notify_peers(struct bonding *bond)
>  	return true;
>  }
>  
> +/* Use this to update send_peer_notif when RTNL may be held in other places. */
> +void bond_peer_notify_work_rearm(struct bonding *bond, unsigned long delay)
> +{
> +	queue_delayed_work(bond->wq, &bond->peer_notify_work, delay);
> +}
> +
> +/* Peer notify update handler. Holds only RTNL */
> +static void bond_peer_notify_reset(struct bonding *bond)
> +{
> +	bond->send_peer_notif = bond->params.num_peer_notif *
> +		max(1, bond->params.peer_notif_delay);
> +}
> +
> +static void bond_peer_notify_handler(struct work_struct *work)
> +{
> +	struct bonding *bond = container_of(work, struct bonding,
> +					    peer_notify_work.work);
> +
> +	if (!rtnl_trylock()) {
> +		bond_peer_notify_work_rearm(bond, 1);
> +		return;
> +	}
> +
> +	bond_peer_notify_reset(bond);
> +
> +	rtnl_unlock();
> +	return;
> +}
> +
>  /**
>   * bond_change_active_slave - change the active slave into the specified one
>   * @bond: our bonding struct
> @@ -1270,8 +1299,6 @@ 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);
>  
> @@ -1279,19 +1306,17 @@ void bond_change_active_slave(struct bonding *bond, struct slave *new_active)
>  				bond_do_fail_over_mac(bond, new_active,
>  						      old_active);
>  
> +			call_netdevice_notifiers(NETDEV_BONDING_FAILOVER, bond->dev);
> +
>  			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);
>  
> -			call_netdevice_notifiers(NETDEV_BONDING_FAILOVER, bond->dev);
> -			if (should_notify_peers) {
> -				bond->send_peer_notif--;
> -				call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
> -							 bond->dev);
> +				if (bond_should_notify_peers(bond)) {
> +					bond->send_peer_notif--;
> +					call_netdevice_notifiers(
> +							NETDEV_NOTIFY_PEERS,
> +							bond->dev);
> +				}
>  			}
>  		}
>  	}
> @@ -4213,6 +4238,10 @@ static u32 bond_xmit_hash_xdp(struct bonding *bond, struct xdp_buff *xdp)
>  
>  void bond_work_init_all(struct bonding *bond)
>  {
> +	/* ndo_stop, bond_close() will try to flush the work under
> +	 * the rtnl lock. The workqueue must not block on rtnl lock
> +	 * to avoid deadlock.
> +	 */
>  	INIT_DELAYED_WORK(&bond->mcast_work,
>  			  bond_resend_igmp_join_requests_delayed);
>  	INIT_DELAYED_WORK(&bond->alb_work, bond_alb_monitor);
> @@ -4220,6 +4249,7 @@ void bond_work_init_all(struct bonding *bond)
>  	INIT_DELAYED_WORK(&bond->arp_work, bond_arp_monitor);
>  	INIT_DELAYED_WORK(&bond->ad_work, bond_3ad_state_machine_handler);
>  	INIT_DELAYED_WORK(&bond->slave_arr_work, bond_slave_arr_handler);
> +	INIT_DELAYED_WORK(&bond->peer_notify_work, bond_peer_notify_handler);
>  }
>  
>  void bond_work_cancel_all(struct bonding *bond)
> @@ -4230,6 +4260,7 @@ void bond_work_cancel_all(struct bonding *bond)
>  	cancel_delayed_work_sync(&bond->ad_work);
>  	cancel_delayed_work_sync(&bond->mcast_work);
>  	cancel_delayed_work_sync(&bond->slave_arr_work);
> +	cancel_delayed_work_sync(&bond->peer_notify_work);
>  }
>  
>  static int bond_open(struct net_device *bond_dev)
> diff --git a/include/net/bonding.h b/include/net/bonding.h
> index 49edc7da0586..63d08056a4a4 100644
> --- a/include/net/bonding.h
> +++ b/include/net/bonding.h
> @@ -254,6 +254,7 @@ struct bonding {
>  	struct   delayed_work ad_work;
>  	struct   delayed_work mcast_work;
>  	struct   delayed_work slave_arr_work;
> +	struct   delayed_work peer_notify_work;
>  #ifdef CONFIG_DEBUG_FS
>  	/* debugging support via debugfs */
>  	struct	 dentry *debug_dir;
> @@ -709,6 +710,7 @@ struct bond_vlan_tag *bond_verify_device_path(struct net_device *start_dev,
>  					      int level);
>  int bond_update_slave_arr(struct bonding *bond, struct slave *skipslave);
>  void bond_slave_arr_work_rearm(struct bonding *bond, unsigned long delay);
> +void bond_peer_notify_work_rearm(struct bonding *bond, unsigned long delay);
>  void bond_work_init_all(struct bonding *bond);
>  void bond_work_cancel_all(struct bonding *bond);
>  
> -- 
> 2.34.1
> 

Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>