netdev - Re: [PATCH net] tcp: avoid fragmenting peculiar skbs in SACK

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Message-ID: <CADVnQynyA-pWE8cWPiiLP_=1tviBNeec97b3HBv_GOMxHZwA_Q@mail.gmail.com>
Date:   Wed, 10 May 2017 21:33:52 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Yuchung Cheng <ycheng@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH net] tcp: avoid fragmenting peculiar skbs in SACK

On Wed, May 10, 2017 at 8:01 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
>
> This patch fixes a bug in splitting an SKB during SACK
> processing. Specifically if an skb contains multiple
> packets and is only partially sacked in the higher sequences,
> tcp_match_sack_to_skb() splits the skb and marks the second fragment
> as SACKed.
>
> The current code further attempts rounding up the first fragment
> to MSS boundaries. But it misses a boundary condition when the
> rounded-up fragment size (pkt_len) is exactly skb size.  Spliting
> such an skb is pointless and causses a kernel warning and aborts
> the SACK processing. This patch universally checks such over-split
> before calling tcp_fragment to prevent these unnecessary warnings.
>
> Fixes: adb92db857ee ("tcp: Make SACK code to split only at mss boundaries")
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Acked-by: Neal Cardwell <ncardwell@...gle.com>

neal