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

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Date:   Mon, 19 Sep 2022 22:39:07 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Sean Anderson <seanga2@...il.com>
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 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.

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.

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