netdev - Re: [PATCH net] bridge: switchdev: Clear forward mark when transmitting packet

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Date:   Fri, 1 Sep 2017 15:03:33 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Ido Schimmel <idosch@...lanox.com>, netdev@...r.kernel.org,
        davem@...emloft.net, stephen@...workplumber.org, jiri@...lanox.com,
        yotamg@...lanox.com, mlxsw@...lanox.com,
        bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net] bridge: switchdev: Clear forward mark when
 transmitting packet

On 01/09/17 15:01, Jiri Pirko wrote:
> Fri, Sep 01, 2017 at 01:45:15PM CEST, nikolay@...ulusnetworks.com wrote:
>> On 01/09/17 12:22, Ido Schimmel wrote:
>>> Commit 6bc506b4fb06 ("bridge: switchdev: Add forward mark support for
>>> stacked devices") added the 'offload_fwd_mark' bit to the skb in order
>>> to allow drivers to indicate to the bridge driver that they already
>>> forwarded the packet in L2.
>>>
>>> In case the bit is set, before transmitting the packet from each port,
>>> the port's mark is compared with the mark stored in the skb's control
>>> block. If both marks are equal, we know the packet arrived from a switch
>>> device that already forwarded the packet and it's not re-transmitted.
>>>
>>> However, if the packet is transmitted from the bridge device itself
>>> (e.g., br0), we should clear the 'offload_fwd_mark' bit as the mark
>>> stored in the skb's control block isn't valid.
>>>
>>> This scenario can happen in rare cases where a packet was trapped during
>>> L3 forwarding and forwarded by the kernel to a bridge device.
>>>
>>> Fixes: 6bc506b4fb06 ("bridge: switchdev: Add forward mark support for stacked devices")
>>> Signed-off-by: Ido Schimmel <idosch@...lanox.com>
>>> Reported-by: Yotam Gigi <yotamg@...lanox.com>
>>> Tested-by: Yotam Gigi <yotamg@...lanox.com>
>>> Reviewed-by: Jiri Pirko <jiri@...lanox.com>
>>> ---
>>>  net/bridge/br_device.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
>>> index 861ae2a165f4..5a7be3bddfa9 100644
>>> --- a/net/bridge/br_device.c
>>> +++ b/net/bridge/br_device.c
>>> @@ -53,6 +53,9 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
>>>  	brstats->tx_bytes += skb->len;
>>>  	u64_stats_update_end(&brstats->syncp);
>>>  
>>> +#ifdef CONFIG_NET_SWITCHDEV
>>> +	skb->offload_fwd_mark = 0;
>>> +#endif
>>>  	BR_INPUT_SKB_CB(skb)->brdev = dev;
>>>  
>>>  	skb_reset_mac_header(skb);
>>>
>>
>> Good catch, just one minor nit since there is already an ifdef
>> switchdev/else in br_private.h, why not make this a helper and avoid the
>> ifdef/endif in here ? Currently there is no ifdef switchdev anywhere else.
> 
> I think it would be better to convert this to a helper in -net-next and
> take the patch as it is for -net
> 

Either way is fine I guess, it's just more work for something as simple. :-)

Whichever way you choose,

Acked-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>