netdev - Re: [PATCH net-next 4/4] bonding: Do not ignore notifications for ARP-work-queue

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Date:	Thu, 12 Mar 2015 17:12:25 +0100
From:	Nikolay Aleksandrov <nikolay@...hat.com>
To:	Mahesh Bandewar <maheshb@...gle.com>,
	Jay Vosburgh <j.vosburgh@...il.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Veaceslav Falico <vfalico@...il.com>,
	David Miller <davem@...emloft.net>
CC:	Maciej Zenczykowski <maze@...gle.com>,
	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next 4/4] bonding: Do not ignore notifications for
 ARP-work-queue

On 03/12/2015 06:54 AM, Mahesh Bandewar wrote:
> This patch adds code to reschedule the ARP-work (aggressively)
> to handle the notifications before resuming the regular cycle.
> 
> Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
> ---
>  drivers/net/bonding/bond_main.c | 38 ++++++++++++++++++++++----------------
>  1 file changed, 22 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 54ecb7a22bae..882974d543d2 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -2814,17 +2814,20 @@ static void bond_activebackup_arp_mon(struct work_struct *work)
>  					    arp_work.work);
>  	bool should_notify_peers = false;
>  	bool should_notify_rtnl = false;
> -	int delta_in_ticks;
> +	unsigned long delta_in_ticks;
>  
>  	delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
>  
>  	if (!bond_has_slaves(bond))
>  		goto re_arm;
>  
> -	rcu_read_lock();
> -
>  	should_notify_peers = bond_should_notify_peers(bond);
> +	if (bond_get_notif_pending(bond, BOND_ARP_NOTIF)) {
> +		rcu_read_lock();
> +		goto eval_arp_probe;
> +	}
>  
> +	rcu_read_lock();
^^^^^^^
Since rcu_read_lock() is acquired in both cases, why don't you leave it
where it is now ? Then you'll be able to save a line and drop the { }
on the "if" above.


>  	if (bond_ab_arp_inspect(bond)) {
>  		rcu_read_unlock();
>  
> @@ -2841,25 +2844,28 @@ static void bond_activebackup_arp_mon(struct work_struct *work)
>  		rcu_read_lock();
>  	}
>  
> +eval_arp_probe:
>  	should_notify_rtnl = bond_ab_arp_probe(bond);
^^^^^
Keep in mind that bond_ab_arp_probe() calls bond_arp_send_all() each time
if we have an active slave. We could be sending ARP requests each tick
until rtnl gets acquired.

>  	rcu_read_unlock();
>  
>  re_arm:
> -	if (bond->params.arp_interval)
> -		queue_delayed_work(bond->wq, &bond->arp_work, delta_in_ticks);
> -
>  	if (should_notify_peers || should_notify_rtnl) {
> -		if (!rtnl_trylock())
> -			return;
> -
> -		if (should_notify_peers)
> -			call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
> -						 bond->dev);
> -		if (should_notify_rtnl)
> -			bond_slave_state_notify(bond);
> -
> -		rtnl_unlock();
> +		if (!rtnl_trylock()) {
> +			delta_in_ticks = 1;
> +			bond_set_notif_pending(bond, BOND_ARP_NOTIF, 1);
> +		} else {
> +			if (should_notify_rtnl)
> +				bond_slave_state_notify(bond);
> +			if (should_notify_peers)
> +				call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
> +							 bond->dev);
> +			rtnl_unlock();
> +			bond_set_notif_pending(bond, BOND_ARP_NOTIF, 0);
> +		}
>  	}
> +
> +	if (bond->params.arp_interval)
> +		queue_delayed_work(bond->wq, &bond->arp_work, delta_in_ticks);
>  }
>  
>  /*-------------------------- netdev event handling --------------------------*/
> 

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