From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: passt.top; dkim=pass (2048-bit key; secure) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.a=rsa-sha256 header.s=202510 header.b=XY7ekZZ2; dkim-atps=neutral Received: from mail.ozlabs.org (gandalf.ozlabs.org [150.107.74.76]) by passt.top (Postfix) with ESMTPS id 1FA2F5A026F for ; Wed, 22 Oct 2025 03:16:58 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202510; t=1761095815; bh=7UsIwGHu7VvkwU343AYA3RsDd6UTOh+rZHtAoS3rFQs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XY7ekZZ20q17NERCG9+djm8xz07TLUzi0Mv1i63CBO6CMcV2u8eQjnB6+U+xUsJ1D b3kRj0PyMc+RX0OObpO5N2xkhI4EvfObEKSseW0482O4T9bKNNh2x3iVRxZr3EikXb XAgxqGWssi3Z3jb5Q8N7Ox51ZDzVtqcidUd1hJ5fdNQ18FV9JDn3krt0WPEK3cORzr DQRNyZ13leJVb4R8WdLxRSn7ix3Ox4xn17DnmFVGJqf3RxNM5+I0umCeULuHy+MVcE AY3gzmAu6QXP9AjCTpvhIqXv++f2aHIhWR7utUCnNrKWwpYmxhFDbncJJQ1bCjDjwp LNzSb+KJskskQ== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4crrqC5jKGz4wCp; Wed, 22 Oct 2025 12:16:55 +1100 (AEDT) Date: Wed, 22 Oct 2025 12:16:51 +1100 From: David Gibson To: Yumei Huang Subject: Re: [PATCH v6 3/4] tcp: Resend SYN for inbound connections Message-ID: References: <20251017062838.21041-1-yuhuang@redhat.com> <20251017062838.21041-4-yuhuang@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="3Qw2r0KZnLI/7Qxk" Content-Disposition: inline In-Reply-To: <20251017062838.21041-4-yuhuang@redhat.com> Message-ID-Hash: 6S4XM4I7OZI7M7EVYTFBFLK26EPEDYO7 X-Message-ID-Hash: 6S4XM4I7OZI7M7EVYTFBFLK26EPEDYO7 X-MailFrom: dgibson@gandalf.ozlabs.org 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: --3Qw2r0KZnLI/7Qxk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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. >=20 > Use the same backoff calculation for the timeout as linux kernel. >=20 > Link: https://bugs.passt.top/show_bug.cgi?id=3D153 > Signed-off-by: Yumei Huang Reviewed-by: David Gibson > --- > tcp.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++-------- > tcp.h | 5 +++++ > 2 files changed, 52 insertions(+), 8 deletions(-) >=20 > 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 fla= gs: > * > - * - SYN_TIMEOUT: if no ACK is received from tap/guest during handshake = (flag > - * ACK_FROM_TAP_DUE without ESTABLISHED event) within this time, reset= the > - * connection > + * - SYN_TIMEOUT_INIT: if no ACK is received from tap/guest during hands= hake > + * (flag ACK_FROM_TAP_DUE without ESTABLISHED event) within this time,= resend > + * SYN. It's the starting timeout for the first SYN retry. If this per= sists > + * 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 s= ending > * data (flag ACK_FROM_TAP_DUE with ESTABLISHED event), re-send data f= rom the > @@ -340,7 +342,7 @@ enum { > #define WINDOW_DEFAULT 14600 /* RFC 6928 */ > =20 > #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_MIGRATE_RCV_QUEUE= _MAX]; > =20 > #define TCP_MIGRATE_RESTORE_CHUNK_MIN 1024 /* Try smaller when above thi= s */ > =20 > +#define TCP_SYN_RETRIES "/proc/sys/net/ipv4/tcp_syn_retries" > +#define TCP_SYN_LINEAR_TIMEOUTS "/proc/sys/net/ipv4/tcp_syn_linear_timeo= uts" \ > + > /* "Extended" data (not stored in the flow table) for TCP flow migration= */ > static struct tcp_tap_transfer_ext migrate_ext[FLOW_MAX]; > =20 > @@ -581,8 +586,13 @@ static void tcp_timer_ctl(const struct ctx *c, struc= t 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_linear_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, union = 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; > } > =20 > +/** > + * tcp_syn_params_init() - Get initial SYN parameters for inbound connec= tion > + * @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%"PRIu= 8, > + c->tcp.tcp_syn_retries, c->tcp.syn_linear_timeouts); > +} > + > /** > * tcp_init() - Get initial sequence, hash secret, initialise per-socket= data > * @c: Execution context > @@ -2776,6 +2813,8 @@ int tcp_init(struct ctx *c) > { > ASSERT(!c->no_tcp); > =20 > + tcp_syn_params_init(c); > + > tcp_sock_iov_init(c); > =20 > 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 packets > * @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 time= out > + * 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; > }; > =20 > #endif /* TCP_H */ > --=20 > 2.47.0 >=20 --=20 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 way | around. http://www.ozlabs.org/~dgibson --3Qw2r0KZnLI/7Qxk Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmj4MIMACgkQzQJF27ox 2GfjGg//braBKXN12EMr4iX6mCVCo20pQemKntI5uFvVBL33h7CCZVN9gHvZhVTf T5wooEwwiDpjek1OnZlcvXkKH6taMZ2JpvUMt6qik5hGu11aZrN7Ut/57a5HNvu7 9UzuikOwp/TvQF/6iMwKWYrfVaoD2efHDOkXrDTIoRiCEZJkFHkV8p+ccm72a4jJ uLpVdKchxwKLzpBogYKUsqBkfKMJMgm+BxusdSM9BzuD5ov75WigJvV/mdTJxGX3 VRoIhBx6JbDs45jnlFxjtYb5CNuEG0Z6LN4c9qQNw9PWBrav6JXq4uK/ktU6EzFb bBxWeMY3OL59xO60xAVrXL1L4m6JnqSU3xgMoCJ0TESi0eI06UZETMRBbCqCNWg1 fz6cZh/Um9VHHMq97EDdrAikibMxRxjo1SooyBo0J1S3BMJ+ViEavzXUooPQnF4X afb+UsojtnEzXPHERZcv/z1XS8N/vWYhvJSE5v52xaL6sk32xh2qaxG51/MiTuio OSxrLm3Fj05A03Yg+jK8+R2WyKrCsetfmSzZTzmPA80Fv11+4bRwtRqPQ1MjZk7C k78bfi8oBQg1wpxsEmEKfGUQqywcnrpX5F/GvYg/EGIF6aarRlTnq334knTFfUfY inLfHSouKMgA50dp/ZrJ2QnxAH6jfq7u4fuoqp1DlW4zLzI3vm8= =bfxp -----END PGP SIGNATURE----- --3Qw2r0KZnLI/7Qxk--