Subject: Re: [PATCH] bonding: Do not try to send packets over dead link in TLB mode.

From: Nikolay Aleksandrov <[email-masked]>
Date: Wed, 09 Jul 2014 12:14:54 +0200

On 07/09/2014 03:09 AM, Mahesh Bandewar wrote:
> In TLB mode if tlb_dynamic_lb is NOT set, slaves from the bond
> group are selected based on the hash distribution. This does not
> exclude dead links which are part of the bond. Also if there is a
> temporary link event which brings down the interface, packets
> hashed on that interface would be dropped too.
> 
> This patch fixes these issues and distributes flows across the
> UP links only. Also the array construction of links which are
> capable of sending packets happen in the control path leaving
> only link-selection duing the data-path.
> 
> One possible side effect of this is - at a link event; all
> flows will be shuffled to get good distribution. But impact of
> this should be minimum with the assumption that a member or
> members of the bond group are not available is a very temporary
> situation.
> 
> Signed-off-by: Mahesh Bandewar <[email-masked]>
> ---

Hi Mahesh,
I think this should be targeted at net-next (and it actually applies there). I
also think you may be able to drop the spinlock as the
bond_alb_handle_link_change() function and its callers are always run under
RTNL, now I'm not 100% sure about this, it would require a more thorough check
but an ASSERT_RTNL at the correct spot could be useful to make sure and convert
anything left, in any case I'm okay as it is now too, this is merely a suggestion.

A few small nitpicks below. I'll give it a spin and if anything pops up will get
back to you.

Thanks for doing this, I like it :-)

>  drivers/net/bonding/bond_alb.c | 52 +++++++++++++++++++++++++++++++++++++-----
>  drivers/net/bonding/bond_alb.h | 11 +++++++++
>  drivers/net/bonding/bonding.h  |  6 +++++
>  3 files changed, 63 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
> index 76c0dade233f..1f39d41fde4b 100644
> --- a/drivers/net/bonding/bond_alb.c
> +++ b/drivers/net/bonding/bond_alb.c
> @@ -195,6 +195,9 @@ static int tlb_initialize(struct bonding *bond)
>  
>  	_unlock_tx_hashtbl_bh(bond);
>  
> +	/* Initialize the TLB array spin-lock */
> +	spin_lock_init(&bond_info->slave_arr_lock);
> +
>  	return 0;
>  }
>  
> @@ -209,6 +212,9 @@ static void tlb_deinitialize(struct bonding *bond)
>  	bond_info->tx_hashtbl = NULL;
>  
>  	_unlock_tx_hashtbl_bh(bond);
> +
> +	if (bond_is_nondyn_tlb(bond) && bond_info->slave_arr)
> +		kfree_rcu(bond_info->slave_arr, rcu);
>  }
>  
>  static long long compute_gap(struct slave *slave)
> @@ -1406,9 +1412,37 @@ out:
>  	return NETDEV_TX_OK;
>  }
>  
> +static int bond_tlb_update_slave_arr(struct bonding *bond)
> +{
> +	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
> +	struct slave *tx_slave;
> +	struct list_head *iter;
> +	struct tlb_up_slave *new_arr, *old_arr;
> +
> +	new_arr = kzalloc(offsetof(struct tlb_up_slave, arr[bond->slave_cnt]),
> +			  GFP_KERNEL);
> +	if (!new_arr)
> +		return -ENOMEM;
> +
> +	bond_for_each_slave(bond, tx_slave, iter) {
> +		if (bond_slave_can_tx(tx_slave))
> +			new_arr->arr[new_arr->count++] = tx_slave;
> +	}
> +
> +	spin_lock(&bond_info->slave_arr_lock);
> +	old_arr = bond_info->slave_arr;
> +	rcu_assign_pointer(bond_info->slave_arr, new_arr);
> +	spin_unlock(&bond_info->slave_arr_lock);
> +	if (old_arr)
> +		kfree_rcu(old_arr, rcu);
> +
> +	return 0;
> +}
> +
>  int bond_tlb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>  {
>  	struct bonding *bond = netdev_priv(bond_dev);
> +	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>  	struct ethhdr *eth_data;
>  	struct slave *tx_slave = NULL;
>  	u32 hash_index;
> @@ -1429,12 +1463,13 @@ int bond_tlb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>  							      hash_index & 0xFF,
>  							      skb->len);
>  			} else {
> -				struct list_head *iter;
> -				int idx = hash_index % bond->slave_cnt;
> -
> -				bond_for_each_slave_rcu(bond, tx_slave, iter)
> -					if (--idx < 0)
> -						break;
> +				struct tlb_up_slave *slaves;
Please leave a blank line between local variable definition and the code.

> +				rcu_read_lock();
All bonding xmit functions already run in rcu, so this is not really necessary.

> +				slaves = rcu_dereference(bond_info->slave_arr);
> +				if (slaves && slaves->count)
> +					tx_slave = slaves->arr[hash_index %
> +							       slaves->count];
> +				rcu_read_unlock();
>  			}
>  			break;
>  		}
> @@ -1721,6 +1756,11 @@ void bond_alb_handle_link_change(struct bonding *bond, struct slave *slave, char
>  			 */
>  		}
>  	}
> +
> +	if (bond_is_nondyn_tlb(bond)) {
> +		if (bond_tlb_update_slave_arr(bond))
> +			pr_err("Failed to build slave-array for TLB mode.\n");
> +	}
>  }
>  
>  /**
> diff --git a/drivers/net/bonding/bond_alb.h b/drivers/net/bonding/bond_alb.h
> index 5fc76c01636c..731a8e830639 100644
> --- a/drivers/net/bonding/bond_alb.h
> +++ b/drivers/net/bonding/bond_alb.h
> @@ -139,12 +139,23 @@ struct tlb_slave_info {
>  			 */
>  };
>  
> +struct tlb_up_slave {
> +	unsigned int	count;
> +	struct rcu_head rcu;
> +	struct slave	*arr[0];
> +};
> +
>  struct alb_bond_info {
>  	struct tlb_client_info	*tx_hashtbl; /* Dynamically allocated */
>  	spinlock_t		tx_hashtbl_lock;
>  	u32			unbalanced_load;
>  	int			tx_rebalance_counter;
>  	int			lp_counter;
> +	/* -------- non-dynamic tlb mode only ---------*/
> +	struct tlb_up_slave __rcu *slave_arr;	  /* Up slaves */
> +	spinlock_t		  slave_arr_lock; /* Lock to manage concurrent
> +						   * writers
> +						   */
>  	/* -------- rlb parameters -------- */
>  	int rlb_enabled;
>  	struct rlb_client_info	*rx_hashtbl;	/* Receive hash table */
> diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
> index 0b4d9cde0b05..ad9b3dce07d8 100644
> --- a/drivers/net/bonding/bonding.h
> +++ b/drivers/net/bonding/bonding.h
> @@ -265,6 +265,12 @@ static inline bool bond_is_lb(const struct bonding *bond)
>  	       BOND_MODE(bond) == BOND_MODE_ALB;
>  }
>  
> +static inline bool bond_is_nondyn_tlb(const struct bonding *bond)
> +{
> +	return (BOND_MODE(bond) == BOND_MODE_TLB)  &&
> +	       (bond->params.tlb_dynamic_lb == 0);
> +}
> +
>  static inline bool bond_mode_uses_arp(int mode)
>  {
>  	return mode != BOND_MODE_8023AD && mode != BOND_MODE_TLB &&
>