netdev - Re: [PATCH v3 2/4] net: Allow for more then a single subclass for netif_addr

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Date:	Wed, 4 Jun 2014 21:42:12 +0000
From:	"Keller, Jacob E" <jacob.e.keller@...el.com>
To:	"vyasevic@...hat.com" <vyasevic@...hat.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"dingtianhong@...wei.com" <dingtianhong@...wei.com>,
	"vfalico@...il.com" <vfalico@...il.com>,
	"kaber@...sh.net" <kaber@...sh.net>,
	"jiri@...nulli.us" <jiri@...nulli.us>
Subject: Re: [PATCH v3 2/4] net: Allow for more then a single subclass for
 netif_addr_lock

On Fri, 2014-05-16 at 17:04 -0400, Vlad Yasevich wrote:
> Currently netif_addr_lock_nested assumes that there can be only
> a single nesting level between 2 devices.  However, if we
> have multiple devices of the same type stacked, this fails.
> For example:
>  eth0 <-- vlan0.10 <-- vlan0.10.20
> 
> A more complicated configuration may stack more then one type of
> device in different order.
> Ex:
>   eth0 <-- vlan0.10 <-- macvlan0 <-- vlan1.10.20 <-- macvlan1
> 
> This patch adds an ndo_* function that allows each stackable
> device to report its nesting level.  If the device doesn't
> provide this function default subclass of 1 is used.
> 
> Signed-off-by: Vlad Yasevich <vyasevic@...hat.com>
> ---
>  include/linux/netdevice.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index fb912e8..9d4b1f1 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1144,6 +1144,7 @@ struct net_device_ops {
>  	netdev_tx_t		(*ndo_dfwd_start_xmit) (struct sk_buff *skb,
>  							struct net_device *dev,
>  							void *priv);
> +	int			(*ndo_get_lock_subclass)(struct net_device *dev);
>  };
>  
>  /**
> @@ -2950,7 +2951,12 @@ static inline void netif_addr_lock(struct net_device *dev)
>  
>  static inline void netif_addr_lock_nested(struct net_device *dev)
>  {
> -	spin_lock_nested(&dev->addr_list_lock, SINGLE_DEPTH_NESTING);
> +	int subclass = SINGLE_DEPTH_NESTING;
> +
> +	if (dev->netdev_ops->ndo_get_lock_subclass)
> +		subclass = dev->netdev_ops->ndo_get_lock_subclass(dev);
> +
> +	spin_lock_nested(&dev->addr_list_lock, subclass);
>  }
>  

Hi,

I know this has already been applied. However, this commit causes a
warning in include/linux/netdevice.h when W=1

In file included from ixgbe/ixgbe.h:35:0,
                 from ixgbe/ixgbe_lib.c:29:
include/linux/netdevice.h: In function ‘netif_addr_lock_nested’:
include/linux/netdevice.h:2954:6: warning: variable ‘subclass’ set but not used [-Wunused-but-set-variable]
  int subclass = SINGLE_DEPTH_NESTING;
      ^

This only occurs if CONFIG_DEBUG_LOCK_ALLOC=Y, and there seems to be no
easy fix for the warning, due to how spin_lock_nested is a macro that
discards the second parameter when DEBUG_LOCK_ALLOC is disabled.

I'm not sure how big a deal this is, considering that it only occurs at
W=1, and the patch is already committed.

>  static inline void netif_addr_lock_bh(struct net_device *dev)

Regards,
Jake