From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: passt.top; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=e8majcBz; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by passt.top (Postfix) with ESMTPS id F1FEC5A026F for ; Wed, 22 Oct 2025 03:31:11 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761096670; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VSPU3MjCwZytHvhzXXwgsTYcpVoA21d5PpCkKd/TeaA=; b=e8majcBznI8RsjgK+8Bc2P/CyGZ4j/RzBgFZ/l8EGq97oyQCrRW+KDWQBFtELqsoO80MJ2 7EES02L+/+SfmTpVf2wIertNcaq6piHvaRhuh6H/XyjmORznjxGadG03mnmjW6E3x8xC5q +7ydyQa/hG/HNkVByKoLmRL4Zfd/6V8= Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-654-S1hp_-HVPcKNHh7MTbF_hA-1; Tue, 21 Oct 2025 21:31:08 -0400 X-MC-Unique: S1hp_-HVPcKNHh7MTbF_hA-1 X-Mimecast-MFC-AGG-ID: S1hp_-HVPcKNHh7MTbF_hA_1761096668 Received: by mail-ed1-f72.google.com with SMTP id 4fb4d7f45d1cf-63c169b6072so6237367a12.2 for ; Tue, 21 Oct 2025 18:31:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761096667; x=1761701467; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=VSPU3MjCwZytHvhzXXwgsTYcpVoA21d5PpCkKd/TeaA=; b=LHSdJ5A2VYoGQ2uo3jyJvek9cEllJwO1+WkV0uSmVOo0PLFqvlJiyYVGjI4aNpkk3f 2IwDi1fUJprrLHycfa5aEEVceUHaXlhg6NoCCPs3mruoaEvcwhb08YLjClDCNQ/vQkpU 34SL9QYDuf27MykBkXVOOThcYlaYJOtZrAxXv4sG3HrFJ6Sk7ZGSbFMHPZO1uc2bR7Fx 9Ql3qqE9McEXHx2kJgpNzwle1Yy2P0f8c/8uyhC9ptwySa9GiePD1Mu20Fvn17gj6NUr K7ErHQ7SO9VK6zJzVcAe1LZGFQD9zDzz7HuP7ZB68viMl/z/BPs8TXPNdx/PrYAOfk1F rKMw== X-Gm-Message-State: AOJu0YzEY09x8lEmVXBnM5kYcKhZgzX0GXVdRO4fOqRhVogDq4jG9fC8 D1XcVy5Rlz+1TjKU668FXDwftB9/P5t8QDhvXZ142JtCWQGPIg+ByMOUuD6HTad+zLANjoRI3lu 5yjw+vfJ6JZBX609ijRpAo3Mdl5peJFoGL1GxDA/EXftsnQKKjccyBZuc7PyrrohVicy2Ja9Min 93zl7MJ6JwFvGAPxZdXF8LB3n/adUKx5oDEHOc X-Gm-Gg: ASbGnct5bPzgMViOCqx/DMINBPGEhRfcsQu9CIryPwmEgFVV/94Z05jjME2OY4O6lJD AMZrepSwRDdKTKH9Dhw9q0wXbGIUxKPrwLqTEZQV314v0PrXdn+iCgAqhXNOkUlY44yZEbjG7w0 L7MYueiolpnregWsgJd98/0JNsUHr7aswonFmMYIsUaS37fS77yZfwyGYv X-Received: by 2002:a05:6402:35c7:b0:63b:ea47:bcbb with SMTP id 4fb4d7f45d1cf-63c1f64c996mr17928735a12.8.1761096667366; Tue, 21 Oct 2025 18:31:07 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHJj9vtj5X2RnJ7ZuEUQNpKk3wieHauPKhP5bp1Sybk0V49ivKaQAC63zmCBxfrjcYtMGk5TnXex22BxRNVd6s= X-Received: by 2002:a05:6402:35c7:b0:63b:ea47:bcbb with SMTP id 4fb4d7f45d1cf-63c1f64c996mr17928708a12.8.1761096666979; Tue, 21 Oct 2025 18:31:06 -0700 (PDT) MIME-Version: 1.0 References: <20251017062838.21041-1-yuhuang@redhat.com> <20251017062838.21041-4-yuhuang@redhat.com> In-Reply-To: From: Yumei Huang Date: Wed, 22 Oct 2025 09:30:55 +0800 X-Gm-Features: AS18NWCbuGhNPf9hwGuFrIecYmMkocK6_gRWFFTBK1WFZXNXWdav1hkvHRkuhJ4 Message-ID: Subject: Re: [PATCH v6 3/4] tcp: Resend SYN for inbound connections To: David Gibson X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 6oIJYxsth3NN1vZgyDnENKisvpldwJLIQ-6NyJRGqYI_1761096668 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Message-ID-Hash: Q6YSVQ2AWQMVGGN3OTCWDRENZSSOHLGJ X-Message-ID-Hash: Q6YSVQ2AWQMVGGN3OTCWDRENZSSOHLGJ X-MailFrom: yuhuang@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top, sbrivio@redhat.com X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Wed, Oct 22, 2025 at 9:17=E2=80=AFAM David Gibson wrote: > > On Fri, Oct 17, 2025 at 02:28:37PM +0800, Yumei Huang wrote: > > If a client connects while guest is not connected or ready yet, > > resend SYN instead of just resetting connection after 10 seconds. > > > > Use the same backoff calculation for the timeout as linux kernel. > > > > Link: https://bugs.passt.top/show_bug.cgi?id=3D153 > > Signed-off-by: Yumei Huang > > Reviewed-by: David Gibson I guess I need to update the doc string for tcp_syn_retries of the struct tcp_ctx, as discussed in v5. Sorry for the inconvenience brought by the multiple versions in a short tim= e. > > > --- > > tcp.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++-------- > > tcp.h | 5 +++++ > > 2 files changed, 52 insertions(+), 8 deletions(-) > > > > diff --git a/tcp.c b/tcp.c > > index 2ec4b0c..9385132 100644 > > --- a/tcp.c > > +++ b/tcp.c > > @@ -179,9 +179,11 @@ > > * > > * Timeouts are implemented by means of timerfd timers, set based on f= lags: > > * > > - * - SYN_TIMEOUT: if no ACK is received from tap/guest during handshak= e (flag > > - * ACK_FROM_TAP_DUE without ESTABLISHED event) within this time, res= et the > > - * connection > > + * - SYN_TIMEOUT_INIT: if no ACK is received from tap/guest during han= dshake > > + * (flag ACK_FROM_TAP_DUE without ESTABLISHED event) within this tim= e, resend > > + * SYN. It's the starting timeout for the first SYN retry. If this p= ersists > > + * for more than TCP_MAX_RETRIES or (tcp_syn_retries + > > + * tcp_syn_linear_timeouts) times in a row, reset the connection > > * > > * - ACK_TIMEOUT: if no ACK segment was received from tap/guest, after= sending > > * data (flag ACK_FROM_TAP_DUE with ESTABLISHED event), re-send data= from the > > @@ -340,7 +342,7 @@ enum { > > #define WINDOW_DEFAULT 14600 /* RFC 69= 28 */ > > > > #define ACK_INTERVAL 10 /* ms */ > > -#define SYN_TIMEOUT 10 /* s */ > > +#define SYN_TIMEOUT_INIT 1 /* s */ > > #define ACK_TIMEOUT 2 > > #define FIN_TIMEOUT 60 > > #define ACT_TIMEOUT 7200 > > @@ -365,6 +367,9 @@ uint8_t tcp_migrate_rcv_queue [TCP_MIGR= ATE_RCV_QUEUE_MAX]; > > > > #define TCP_MIGRATE_RESTORE_CHUNK_MIN 1024 /* Try smaller when = above this */ > > > > +#define TCP_SYN_RETRIES "/proc/sys/net/ipv4/tcp_syn_retri= es" > > +#define TCP_SYN_LINEAR_TIMEOUTS "/proc/sys/net/ipv4/tcp_syn_linea= r_timeouts" \ > > + > > /* "Extended" data (not stored in the flow table) for TCP flow migrati= on */ > > static struct tcp_tap_transfer_ext migrate_ext[FLOW_MAX]; > > > > @@ -581,8 +586,13 @@ static void tcp_timer_ctl(const struct ctx *c, str= uct tcp_tap_conn *conn) > > if (conn->flags & ACK_TO_TAP_DUE) { > > it.it_value.tv_nsec =3D (long)ACK_INTERVAL * 1000 * 1000; > > } else if (conn->flags & ACK_FROM_TAP_DUE) { > > - if (!(conn->events & ESTABLISHED)) > > - it.it_value.tv_sec =3D SYN_TIMEOUT; > > + if (!(conn->events & ESTABLISHED)) { > > + if (conn->retries < c->tcp.syn_linear_timeouts) > > + it.it_value.tv_sec =3D SYN_TIMEOUT_INIT; > > + else > > + it.it_value.tv_sec =3D SYN_TIMEOUT_INIT <= < > > + (conn->retries - c->tcp.syn_linea= r_timeouts); > > + } > > else > > it.it_value.tv_sec =3D ACK_TIMEOUT; > > } else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED)) { > > @@ -2409,8 +2419,17 @@ void tcp_timer_handler(const struct ctx *c, unio= n epoll_ref ref) > > tcp_timer_ctl(c, conn); > > } else if (conn->flags & ACK_FROM_TAP_DUE) { > > if (!(conn->events & ESTABLISHED)) { > > - flow_dbg(conn, "handshake timeout"); > > - tcp_rst(c, conn); > > + if (conn->retries >=3D TCP_MAX_RETRIES || > > + conn->retries >=3D (c->tcp.tcp_syn_retries + > > + c->tcp.syn_linear_timeouts)= ) { > > + flow_dbg(conn, "handshake timeout"); > > + tcp_rst(c, conn); > > + } else { > > + flow_trace(conn, "SYN timeout, retry"); > > + tcp_send_flag(c, conn, SYN); > > + conn->retries++; > > + tcp_timer_ctl(c, conn); > > + } > > } else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED))= { > > flow_dbg(conn, "FIN timeout"); > > tcp_rst(c, conn); > > @@ -2766,6 +2785,24 @@ static socklen_t tcp_probe_tcp_info(void) > > return sl; > > } > > > > +/** > > + * tcp_syn_params_init() - Get initial SYN parameters for inbound conn= ection > > + * @c: Execution context > > +*/ > > +void tcp_syn_params_init(struct ctx *c) > > +{ > > + intmax_t tcp_syn_retries, syn_linear_timeouts; > > + > > + tcp_syn_retries =3D read_file_integer(TCP_SYN_RETRIES, 8); > > + syn_linear_timeouts =3D read_file_integer(TCP_SYN_LINEAR_TIMEOUTS= , 1); > > + > > + c->tcp.tcp_syn_retries =3D MIN(tcp_syn_retries, UINT8_MAX); > > + c->tcp.syn_linear_timeouts =3D MIN(syn_linear_timeouts, UINT8_MAX= ); > > + > > + debug("TCP SYN parameters: retries=3D%"PRIu8", linear_timeouts=3D= %"PRIu8, > > + c->tcp.tcp_syn_retries, c->tcp.syn_linear_timeouts); > > +} > > + > > /** > > * tcp_init() - Get initial sequence, hash secret, initialise per-sock= et data > > * @c: Execution context > > @@ -2776,6 +2813,8 @@ int tcp_init(struct ctx *c) > > { > > ASSERT(!c->no_tcp); > > > > + tcp_syn_params_init(c); > > + > > tcp_sock_iov_init(c); > > > > memset(init_sock_pool4, 0xff, sizeof(init_sock_pool4)); > > diff --git a/tcp.h b/tcp.h > > index 234a803..4369b52 100644 > > --- a/tcp.h > > +++ b/tcp.h > > @@ -59,12 +59,17 @@ union tcp_listen_epoll_ref { > > * @fwd_out: Port forwarding configuration for outbound packet= s > > * @timer_run: Timestamp of most recent timer run > > * @pipe_size: Size of pipes for spliced connections > > + * @tcp_syn_retries: Number of SYN retries during handshake > > + * @syn_linear_timeouts: Number of SYN retries using linear backoff ti= meout > > + * before switching to exponential backoff timeout > > */ > > struct tcp_ctx { > > struct fwd_ports fwd_in; > > struct fwd_ports fwd_out; > > struct timespec timer_run; > > size_t pipe_size; > > + uint8_t tcp_syn_retries; > > + uint8_t syn_linear_timeouts; > > }; > > > > #endif /* TCP_H */ > > -- > > 2.47.0 > > > > -- > David Gibson (he or they) | I'll have my music baroque, and my code > david AT gibson.dropbear.id.au | minimalist, thank you, not the other wa= y > | around. > http://www.ozlabs.org/~dgibson -- Thanks, Yumei Huang