netdev - Re: [PATCH net] tcp: do not send empty skb from tcp_write

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Date:   Wed, 11 Dec 2019 15:05:01 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Christoph Paasch <cpaasch@...le.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH net] tcp: do not send empty skb from tcp_write_xmit()

On Wed, Dec 11, 2019 at 2:34 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Backport of commit fdfc5c8594c2 ("tcp: remove empty skb from
> write queue in error cases") in linux-4.14 stable triggered
> various bugs. One of them has been fixed in commit ba2ddb43f270
> ("tcp: Don't dequeue SYN/FIN-segments from write-queue"), but
> we still have crashes in some occasions.
>
> Root-cause is that when tcp_sendmsg() has allocated a fresh
> skb and could not append a fragment before being blocked
> in sk_stream_wait_memory(), tcp_write_xmit() might be called
> and decide to send this fresh and empty skb.
>
> Sending an empty packet is not only silly, it might have caused
> many issues we had in the past with tp->packets_out being
> out of sync.
>
> Fixes: c65f7f00c587 ("[TCP]: Simplify SKB data portion allocation with NETIF_F_SG.")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Christoph Paasch <cpaasch@...le.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Cc: Jason Baron <jbaron@...mai.com>
> ---

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

thanks,
neal