From: Eric Dumazet <edumazet@google.com>
To: Alexander Duyck <alexander.duyck@gmail.com>
Cc: David Miller <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Yuchung Cheng <ycheng@google.com>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Martin KaFai Lau <kafai@fb.com>, kernel-team <kernel-team@fb.com>
Subject: Re: [net-next PATCH v3] tcp: Add logic to check for SYN w/ data in tcp_simple_retransmit
Date: Mon, 14 Dec 2020 18:42:42 +0100 [thread overview]
Message-ID: <CANn89i+uQ0p81O3-aWO-WPifc35KtpDFRsO9WJKrXxEhpArDWw@mail.gmail.com> (raw)
In-Reply-To: <160780498125.3272.15437756269539236825.stgit@localhost.localdomain>
On Sat, Dec 12, 2020 at 9:31 PM Alexander Duyck
<alexander.duyck@gmail.com> wrote:
>
> From: Alexander Duyck <alexanderduyck@fb.com>
>
> There are cases where a fastopen SYN may trigger either a ICMP_TOOBIG
> message in the case of IPv6 or a fragmentation request in the case of
> IPv4. This results in the socket stalling for a second or more as it does
> not respond to the message by retransmitting the SYN frame.
>
> Normally a SYN frame should not be able to trigger a ICMP_TOOBIG or
> ICMP_FRAG_NEEDED however in the case of fastopen we can have a frame that
> makes use of the entire MSS. In the case of fastopen it does, and an
> additional complication is that the retransmit queue doesn't contain the
> original frames. As a result when tcp_simple_retransmit is called and
> walks the list of frames in the queue it may not mark the frames as lost
> because both the SYN and the data packet each individually are smaller than
> the MSS size after the adjustment. This results in the socket being stalled
> until the retransmit timer kicks in and forces the SYN frame out again
> without the data attached.
>
> In order to resolve this we can reduce the MSS the packets are compared
> to in tcp_simple_retransmit to -1 for cases where we are still in the
> TCP_SYN_SENT state for a fastopen socket. Doing this we will mark all of
> the packets related to the fastopen SYN as lost.
>
> Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
> ---
>
SGTM, thanks !
Signed-off-by: Eric Dumazet <edumazet@google.com>
> v2: Changed logic to invalidate all retransmit queue frames if fastopen SYN
> v3: Updated commit message to reflect actual solution in 3rd paragraph
>
next prev parent reply other threads:[~2020-12-14 17:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-12 20:31 [net-next PATCH v3] tcp: Add logic to check for SYN w/ data in tcp_simple_retransmit Alexander Duyck
2020-12-14 17:42 ` Eric Dumazet [this message]
2020-12-14 18:52 ` Yuchung Cheng
2020-12-15 3:40 ` patchwork-bot+netdevbpf
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