netdev - Re: [PATCH v2 net-next] vlan: Add GRO support for non hardware accelerated vlan

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Date:	Mon, 01 Jun 2015 07:12:37 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Cc:	"David S . Miller" <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next] vlan: Add GRO support for non hardware
 accelerated vlan

On Mon, 2015-06-01 at 21:55 +0900, Toshiaki Makita wrote:

> @@ -668,6 +753,9 @@ static int __init vlan_proto_init(void)
>  	if (err < 0)
>  		goto err5;
>  
> +	for (i = 0; i < ARRAY_SIZE(vlan_packet_offloads); i++)
> +		dev_add_offload(&vlan_packet_offloads[i]);
> +
>  	vlan_ioctl_set(vlan_ioctl_handler);
>  	return 0;

My concern about this is :

This might slow down GRO stack for other traffic, if dev_add_offload()
for vlan offloads is called after 
dev_add_offload(&ip_packet_offload) /
dev_add_offload(&ipv6_packet_offload)


This is because list_add_rcu is used and this inserts in front of the
offload_base list.

void dev_add_offload(struct packet_offload *po)
{
        struct list_head *head = &offload_base;

        spin_lock(&offload_lock);
        list_add_rcu(&po->list, head);
        spin_unlock(&offload_lock);
}

Can we ensure offload_base contains a sensible order of expected types ?


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