linux-kernel - Re: [PATCH] net: sunhme: Fix packet reception for len < RX_COPY

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Date:   Mon, 19 Sep 2022 20:31:23 -0400
From:   Sean Anderson <seanga2@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Zheyu Ma <zheyuma97@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        Rolf Eike Beer <eike-kernel@...tec.de>,
        Nick Bowler <nbowler@...conx.ca>
Subject: Re: [PATCH] net: sunhme: Fix packet reception for len <
 RX_COPY_THRESHOLD

On 9/19/22 16:39, Andrew Lunn wrote:
> On Sun, Sep 18, 2022 at 05:55:34PM -0400, Sean Anderson wrote:
>> There is a separate receive path for small packets (under 256 bytes).
>> Instead of allocating a new dma-capable skb to be used for the next packet,
>> this path allocates a skb and copies the data into it (reusing the existing
>> sbk for the next packet). There are two bytes of junk data at the beginning
>> of every packet. I believe these are inserted in order to allow aligned
>> DMA and IP headers. We skip over them using skb_reserve. Before copying
>> over the data, we must use a barrier to ensure we see the whole packet. The
>> current code only synchronizes len bytes, starting from the beginning of
>> the packet, including the junk bytes. However, this leaves off the final
>> two bytes in the packet. Synchronize the whole packet.
>>
>> To reproduce this problem, ping a HME with a payload size between 17 and 214
>>
>> 	$ ping -s 17 <hme_address>
>>
>> which will complain rather loudly about the data mismatch. Small packets
>> (below 60 bytes on the wire) do not have this issue. I suspect this is
>> related to the padding added to increase the minimum packet size.
>>
>> Signed-off-by: Sean Anderson <seanga2@...il.com>
> 
> Hi Sean
> 
>> Patch-prefix: net
> 
> This should be in the Subject of the email. Various tools look for the
> netdev tree there. Please try to remember that for future patches.

Sorry, it should have been "Series-postfix".

> Please could you add a Fixes: tag indicating when the problem was
> introduced. Its O.K. if that was when the driver was added. It just
> helps getting the patch back ported to older stable kernels.

Well, the driver was added before git was started...

I suppose I could blame 1da177e4c3f4 ("Linux-2.6.12-rc2"), but maybe I
should just CC the stable list?

> I think patchwork allows you to just reply to your post, and it will
> automagically append the Fixes: tag when the Maintainer actually
> applies the patch.
> 
> Reviewed-by: Andrew Lunn <andrew@...n.ch>
> 
>      Andrew

--Sean