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

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Message-ID: <20170901120120.GA1962@nanopsycho>
Date:   Fri, 1 Sep 2017 14:01:20 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
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

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