From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86C79C433E6 for ; Wed, 13 Jan 2021 21:25:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 459672310A for ; Wed, 13 Jan 2021 21:25:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729070AbhAMVYC (ORCPT ); Wed, 13 Jan 2021 16:24:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729087AbhAMVWP (ORCPT ); Wed, 13 Jan 2021 16:22:15 -0500 Received: from mail-wr1-x431.google.com (mail-wr1-x431.google.com [IPv6:2a00:1450:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C36A6C061575 for ; Wed, 13 Jan 2021 13:21:33 -0800 (PST) Received: by mail-wr1-x431.google.com with SMTP id y17so3610858wrr.10 for ; Wed, 13 Jan 2021 13:21:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Ba13zS/5BmLfosyFnrfPCCq9Y7pVaB7VwGsd4lLySYc=; b=uACgDp8Xqrq7HRZmhdGjo7eqo2yY6VzFeCp2TI2kvgM9DLfpNIWHLlaLH7zsO+ilik T0jqhUWJb/syBsCaCx42vHroqV5qbM0iNcCvSz58Y3O0DlWKt+qKEQMUw2A8McLglQBs 2v/Hg4qp5d7zHEHZqSFASykiYZbmji9VfudWN59TkBCnmjK7pv/TwwPgnFC1TAQk479q 0Y62S7+hPLEmwPm5mDR2CLDK0e2Gv0ykMNql6OVXMy1cCn9WTyOBUNhO5EFWmlmpVNHx S6UPp/cIbTQN/y+ouzat/sEeLuWGhCL8xtlaNWtwHAcVRhrPJU4847E0okNRlS3ZvFqf yNuA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Ba13zS/5BmLfosyFnrfPCCq9Y7pVaB7VwGsd4lLySYc=; b=thy/ipAT0pVjJwlrFRHVC/PCMQbxJT7c21Dx6bA4IW/7Tk6/dcFjJTwZet4mmYAxa/ HrQr+CGH1BEyXO6+LxJYxLz/fWwS82YH0c13t4xE9/Yh0fVcMn8azvHpcIf2bbgLPHay sbR/XFTSi2SAtzUO1FtIclu781gclw/BdtsxREu46EvTM0E2pLY+chUY9rktBQ/Sw6q7 PnHq3aSVympb4QdwAzauFaqKYtntFEU1J/G9NdnaFUM51bLZqwB4/jtcAqoiIEyqYFc2 1Fa38c3Rx+q/IBd5YkWIsCpdcO+EfZlWZys+aV4XGUYy+BuBROUB9glT2qPdZNtw7dB6 THVA== X-Gm-Message-State: AOAM533dKjv7LLuaAYv6pMFwBs8YucXAx742dK0RhH8jrPeCIOIIjdlA 82irXQhvcwRyoLa+i2srmKceLf8D3WljFIl32fJsBStAl+w= X-Google-Smtp-Source: ABdhPJxsJLzpd9Z/Kg9wRhljmpHCgKSDrOPR64ZQEJwRh/ftdQHF/0gEz72ZO05FZ/5eZGFZ1S3mYHJhO0hxURPJPTc= X-Received: by 2002:adf:dc8b:: with SMTP id r11mr4584912wrj.131.1610572892263; Wed, 13 Jan 2021 13:21:32 -0800 (PST) MIME-Version: 1.0 References: <20210113201201.GC2274@localhost.localdomain> In-Reply-To: From: Yuchung Cheng Date: Wed, 13 Jan 2021 13:20:55 -0800 Message-ID: Subject: Re: [PATCH] tcp: fix TCP_USER_TIMEOUT with zero window To: Eric Dumazet Cc: Enke Chen , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Jakub Kicinski , netdev , LKML , Jonathan Maxwell , William McCall Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Jan 13, 2021 at 12:49 PM Eric Dumazet wrote: > > On Wed, Jan 13, 2021 at 9:12 PM Enke Chen wrote: > > > > From: Enke Chen > > > > The TCP session does not terminate with TCP_USER_TIMEOUT when data > > remain untransmitted due to zero window. > > > > The number of unanswered zero-window probes (tcp_probes_out) is > > reset to zero with incoming acks irrespective of the window size, > > as described in tcp_probe_timer(): > > > > RFC 1122 4.2.2.17 requires the sender to stay open indefinitely > > as long as the receiver continues to respond probes. We support > > this by default and reset icsk_probes_out with incoming ACKs. > > > > This counter, however, is the wrong one to be used in calculating the > > duration that the window remains closed and data remain untransmitted. > > Thanks to Jonathan Maxwell for diagnosing the > > actual issue. > > > > In this patch a separate counter is introduced to track the number of > > zero-window probes that are not answered with any non-zero window ack. > > This new counter is used in determining when to abort the session with > > TCP_USER_TIMEOUT. > > > > I think one possible issue would be that local congestion (full qdisc) > would abort early, > because tcp_model_timeout() assumes linear backoff. Yes exactly. if ZWPs are dropped due to local congestion, the model_timeout computes incorrectly. Therefore having a starting timestamp is the surest way b/c it does not assume any specific backoff behavior. > > Neal or Yuchung can further comment on that, it is late for me in France. > > packetdrill test would be : > > 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 > +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 > +0 bind(3, ..., ...) = 0 > +0 listen(3, 1) = 0 > > > +0 < S 0:0(0) win 0 > +0 > S. 0:0(0) ack 1 > > +.1 < . 1:1(0) ack 1 win 65530 > +0 accept(3, ..., ...) = 4 > > +0 setsockopt(4, SOL_TCP, TCP_USER_TIMEOUT, [3000], 4) = 0 > +0 write(4, ..., 24) = 24 > +0 > P. 1:25(24) ack 1 > +.1 < . 1:1(0) ack 25 win 65530 > +0 %{ assert tcpi_probes == 0, tcpi_probes; \ > assert tcpi_backoff == 0, tcpi_backoff }% > > // install a qdisc dropping all packets > +0 `tc qdisc delete dev tun0 root 2>/dev/null ; tc qdisc add dev > tun0 root pfifo limit 0` > +0 write(4, ..., 24) = 24 > // When qdisc is congested we retry every 500ms therefore in theory > // we'd retry 6 times before hitting 3s timeout. However, since we > // estimate the elapsed time based on exp backoff of actual RTO (300ms), > // we'd bail earlier with only 3 probes. > +2.1 write(4, ..., 24) = -1 > +0 %{ assert tcpi_probes == 3, tcpi_probes; \ > assert tcpi_backoff == 0, tcpi_backoff }% > +0 close(4) = 0 > > > Cc: stable@vger.kernel.org > > Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT") > > Reported-by: William McCall > > Signed-off-by: Enke Chen > > --- > > include/linux/tcp.h | 5 +++++ > > net/ipv4/tcp.c | 1 + > > net/ipv4/tcp_input.c | 3 ++- > > net/ipv4/tcp_output.c | 2 ++ > > net/ipv4/tcp_timer.c | 5 +++-- > > 5 files changed, 13 insertions(+), 3 deletions(-) > > > > diff --git a/include/linux/tcp.h b/include/linux/tcp.h > > index 2f87377e9af7..c9415b30fa67 100644 > > --- a/include/linux/tcp.h > > +++ b/include/linux/tcp.h > > @@ -352,6 +352,11 @@ struct tcp_sock { > > > > int linger2; > > > > + /* While icsk_probes_out is for unanswered 0 window probes, this > > + * counter is for 0-window probes that are not answered with any > > + * non-zero window (nzw) acks. > > + */ > > + u8 probes_nzw; > > > > /* Sock_ops bpf program related variables */ > > #ifdef CONFIG_BPF > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > > index ed42d2193c5c..af6a41a5a5ac 100644 > > --- a/net/ipv4/tcp.c > > +++ b/net/ipv4/tcp.c > > @@ -2940,6 +2940,7 @@ int tcp_disconnect(struct sock *sk, int flags) > > icsk->icsk_rto = TCP_TIMEOUT_INIT; > > icsk->icsk_rto_min = TCP_RTO_MIN; > > icsk->icsk_delack_max = TCP_DELACK_MAX; > > + tp->probes_nzw = 0; > > tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; > > tp->snd_cwnd = TCP_INIT_CWND; > > tp->snd_cwnd_cnt = 0; > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > > index c7e16b0ed791..4812a969c18a 100644 > > --- a/net/ipv4/tcp_input.c > > +++ b/net/ipv4/tcp_input.c > > @@ -3377,13 +3377,14 @@ static void tcp_ack_probe(struct sock *sk) > > { > > struct inet_connection_sock *icsk = inet_csk(sk); > > struct sk_buff *head = tcp_send_head(sk); > > - const struct tcp_sock *tp = tcp_sk(sk); > > + struct tcp_sock *tp = tcp_sk(sk); > > > > /* Was it a usable window open? */ > > if (!head) > > return; > > if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) { > > icsk->icsk_backoff = 0; > > + tp->probes_nzw = 0; > > inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0); > > /* Socket must be waked up by subsequent tcp_data_snd_check(). > > * This function is not for random using! > > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c > > index f322e798a351..1b64cdabc299 100644 > > --- a/net/ipv4/tcp_output.c > > +++ b/net/ipv4/tcp_output.c > > @@ -4084,10 +4084,12 @@ void tcp_send_probe0(struct sock *sk) > > /* Cancel probe timer, if it is not required. */ > > icsk->icsk_probes_out = 0; > > icsk->icsk_backoff = 0; > > + tp->probes_nzw = 0; > > return; > > } > > > > icsk->icsk_probes_out++; > > + tp->probes_nzw++; > > if (err <= 0) { > > if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2) > > icsk->icsk_backoff++; > > diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c > > index 6c62b9ea1320..87e9f5998b8e 100644 > > --- a/net/ipv4/tcp_timer.c > > +++ b/net/ipv4/tcp_timer.c > > @@ -349,6 +349,7 @@ static void tcp_probe_timer(struct sock *sk) > > > > if (tp->packets_out || !skb) { > > icsk->icsk_probes_out = 0; > > + tp->probes_nzw = 0; > > return; > > } > > > > @@ -360,8 +361,8 @@ static void tcp_probe_timer(struct sock *sk) > > * corresponding system limit. We also implement similar policy when > > * we use RTO to probe window in tcp_retransmit_timer(). > > */ > > - if (icsk->icsk_user_timeout) { > > - u32 elapsed = tcp_model_timeout(sk, icsk->icsk_probes_out, > > + if (icsk->icsk_user_timeout && tp->probes_nzw) { > > + u32 elapsed = tcp_model_timeout(sk, tp->probes_nzw, > > tcp_probe0_base(sk)); > > > > if (elapsed >= icsk->icsk_user_timeout) > > -- > > 2.29.2 > >