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=qoMKYxCv; dkim-atps=neutral Received: from mail.ozlabs.org (gandalf.ozlabs.org [150.107.74.76]) by passt.top (Postfix) with ESMTPS id 8EB2B5A0619 for ; Wed, 15 Oct 2025 02:05:11 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202510; t=1760486709; bh=1jpDkrRWuSty39dRo1XcIlkwyEyt449Tw/bLDziuxPk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qoMKYxCv4guHASKvnUJyJdrY9d/4CS0Jpcpri6QUP3SSrTbsXzekqNiQof4K/qfaY 4EyQ9ESY4vWfOK36cdOOUO91KknAVvbFTdK8fuPeaU0qzhx5Blg+8pB68d+/eEk41C yCkXuNWedhaNTeC9C0L4/1oHi7yq5SSOB+ZHxhKnvELN+gBg/17qX9FSLewLLVAZNc K9r6lTHjOhTP2FEPZ0ExkGRjkhpq712C0tECDl6FVtG9uh4E1HXCxTqigrLQidBvzH yazIMbNwJ0B88dxiTPW43aMI/pGu/BQC4OdJ2bhw42lmZRZm9dE5URfpSwkEU/ytwS 2UjQz9MXx1bDQ== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4cmWYd39wwz4wBB; Wed, 15 Oct 2025 11:05:09 +1100 (AEDT) Date: Wed, 15 Oct 2025 10:40:11 +1100 From: David Gibson To: Yumei Huang Subject: Re: [PATCH v3 3/4] tcp: Resend SYN for inbound connections Message-ID: References: <20251014073836.18150-1-yuhuang@redhat.com> <20251014073836.18150-4-yuhuang@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="Q4qzvzA3Sp6woT4U" Content-Disposition: inline In-Reply-To: <20251014073836.18150-4-yuhuang@redhat.com> Message-ID-Hash: T3IMF5KNGZDLCJSCMDRCRCDB6U6K56OJ X-Message-ID-Hash: T3IMF5KNGZDLCJSCMDRCRCDB6U6K56OJ 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: --Q4qzvzA3Sp6woT4U Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Oct 14, 2025 at 03:38:35PM +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 > Signed-off-by: Yumei Huang Reviewed-by: David Gibson A few cosmetic nits noted below. > --- > tcp.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++-------- > tcp.h | 2 ++ > 2 files changed, 49 insertions(+), 8 deletions(-) >=20 > diff --git a/tcp.c b/tcp.c > index 2ec4b0c..3ce3991 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 +367,10 @@ uint8_t tcp_migrate_rcv_queue [TCP_MIGRATE_RCV_QUEU= E_MAX]; > =20 > #define TCP_MIGRATE_RESTORE_CHUNK_MIN 1024 /* Try smaller when above thi= s */ > =20 > +#define TCP_SYN_RETRIES_SYSCTL "/proc/sys/net/ipv4/tcp_syn_retries" > +#define TCP_SYN_LINEAR_TIMEOUTS_SYSCTL \ > + "/proc/sys/net/ipv4/tcp_syn_linear_timeouts" > + > /* "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 +587,13 @@ 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 +2420,16 @@ 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 MIN(TCP_MAX_RETRIES, > + (c->tcp.tcp_syn_retries + c->tcp.syn_linear_timeouts))) { > + flow_dbg(conn, "handshake timeout"); > + tcp_rst(c, conn); > + } else { > + flow_dbg(conn, "SYN timeout, retry"); I'd suggest demoting this to flow_trace() since it can occur on a perfectly ok connection. > + 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 params for inbound connection > + * @c: Execution context > +*/ > +void tcp_syn_params_init(struct ctx *c) > +{ > + long tcp_syn_retries, syn_linear_timeouts; > + > + tcp_syn_retries =3D read_file_long(TCP_SYN_RETRIES_SYSCTL, 8); > + syn_linear_timeouts =3D read_file_long(TCP_SYN_LINEAR_TIMEOUTS_SYSCTL, = 1); > + > + c->tcp.tcp_syn_retries =3D (uint8_t)MIN(tcp_syn_retries, UINT8_MAX); > + c->tcp.syn_linear_timeouts =3D (uint8_t)MIN(syn_linear_timeouts, UINT8_= MAX); > + > + debug("TCP SYN parameters: retries=3D%d, linear_timeouts=3D%d", > + c->tcp.tcp_syn_retries, c->tcp.syn_linear_timeouts); This will work because of the (somewhat arcane) promotion rules for variadic functions. It would be more correct to use the PRIu8 define =66rom inttypes.h, since the parameters are uint8_t (grep for "PRIu" to see examples of how these defines are used). > +} > + > /** > * 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..df699a4 100644 > --- a/tcp.h > +++ b/tcp.h > @@ -65,6 +65,8 @@ struct tcp_ctx { > 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 --Q4qzvzA3Sp6woT4U Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmju31oACgkQzQJF27ox 2Gc8nxAAqapZsmp3mtsdvuhg96aX61yr61ggohEjzAK1+UrRWEtGjJUYBWX+EWaS KU0R2+MYJkbLKn8KoloekrbG/j++IF9nz4onS8MzdU/YuN5VYiCxrven+vjPBK73 16B6WpTW622o17ci81UqEQKIjUQINX8faK3QI6NaI6RdCRhbdda7/UnGyuFnjhyT ywxXPJx+4HsdhrVEe4Cj+dLcqNp34eaPdg31/Qf0zPxBllFREKbbCVcMMPLLnCeJ 3kJCUQjrF+0ua5F9Rfc79l9s9PYF6QAkuB2m5ushhBy6dA4Lzhxc4+cXqDO+GaJg ZvvKg8R9s0hmTxYf0IozpqUY93cjtdXtk/0Y/B2bbZ8eTofJ0fabRm8hPIKL3IuB jxjge1gPo6MtoIBFk9BanN1qVrwEnVJQm8nQM1FNo3/vP48XAHvrTwJhy463GjtL /l7wWXSdhfHUlMA4inwT6gIU5HyUBVcdvnvLSv0b8CtUYtjJttoe6zTVBi5jOSBH B78kpglRmwke1hOnqfvybb+edWpYsKAawzgRfUCZu60LEWix+NTiv4h9PGcltuPz UolWVwxH5tNy46YH4SWdsjK06pkgEKoWg0dI9bAbVgneNydn/lAyNIhGnse48nYv GbAK2Gx8g4c8xa9uOc47FKfYsaiNwOq+BB+xBbtn48bw999OgKY= =2yjY -----END PGP SIGNATURE----- --Q4qzvzA3Sp6woT4U--