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=UFnmLdvE; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTPS id 70B535A026F for ; Fri, 17 Oct 2025 08:29:06 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760682545; 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=27SM/stICsMtg2lMst0fJP4ukyugxIqXy1Byq4xAcAA=; b=UFnmLdvEt+AhQ2dagFmPl1CYggnDid8HEdguxnqnuZbkConBJW8l4PVnDRWV2Z5cDhuHwy ow9q0iPn0PfH4TXP+gGRGVqOCpeWDV2pKzLYduCJTOsb5xzpdfMu8RbsYIXen8DUkny3n6 XhMexVXxuXSUADlpQwT8x5LRdMs/i84= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-269-QeNd0XQnPS6vQU9w-DU34w-1; Fri, 17 Oct 2025 02:29:04 -0400 X-MC-Unique: QeNd0XQnPS6vQU9w-DU34w-1 X-Mimecast-MFC-AGG-ID: QeNd0XQnPS6vQU9w-DU34w_1760682543 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 59AF1195608A; Fri, 17 Oct 2025 06:29:03 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.72.112.60]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B52C51956056; Fri, 17 Oct 2025 06:28:59 +0000 (UTC) From: Yumei Huang To: passt-dev@passt.top, sbrivio@redhat.com Subject: [PATCH v6 3/4] tcp: Resend SYN for inbound connections Date: Fri, 17 Oct 2025 14:28:37 +0800 Message-ID: <20251017062838.21041-4-yuhuang@redhat.com> In-Reply-To: <20251017062838.21041-1-yuhuang@redhat.com> References: <20251017062838.21041-1-yuhuang@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 0xSnXmQHX3xVJOgKL9CiJu64gc6L5I06oGwFkTh5P8s_1760682543 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true Message-ID-Hash: KRIPTI5LIJVZRALHXFTPP4PMZPEREVZO X-Message-ID-Hash: KRIPTI5LIJVZRALHXFTPP4PMZPEREVZO 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: david@gibson.dropbear.id.au, yuhuang@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: 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=153 Signed-off-by: Yumei Huang --- 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 flags: * - * - 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 handshake + * (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 persists + * 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 6928 */ #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]; #define TCP_MIGRATE_RESTORE_CHUNK_MIN 1024 /* Try smaller when above this */ +#define TCP_SYN_RETRIES "/proc/sys/net/ipv4/tcp_syn_retries" +#define TCP_SYN_LINEAR_TIMEOUTS "/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]; @@ -581,8 +586,13 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn *conn) if (conn->flags & ACK_TO_TAP_DUE) { it.it_value.tv_nsec = (long)ACK_INTERVAL * 1000 * 1000; } else if (conn->flags & ACK_FROM_TAP_DUE) { - if (!(conn->events & ESTABLISHED)) - it.it_value.tv_sec = SYN_TIMEOUT; + if (!(conn->events & ESTABLISHED)) { + if (conn->retries < c->tcp.syn_linear_timeouts) + it.it_value.tv_sec = SYN_TIMEOUT_INIT; + else + it.it_value.tv_sec = SYN_TIMEOUT_INIT << + (conn->retries - c->tcp.syn_linear_timeouts); + } else it.it_value.tv_sec = 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 >= TCP_MAX_RETRIES || + conn->retries >= (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 connection + * @c: Execution context +*/ +void tcp_syn_params_init(struct ctx *c) +{ + intmax_t tcp_syn_retries, syn_linear_timeouts; + + tcp_syn_retries = read_file_integer(TCP_SYN_RETRIES, 8); + syn_linear_timeouts = read_file_integer(TCP_SYN_LINEAR_TIMEOUTS, 1); + + c->tcp.tcp_syn_retries = MIN(tcp_syn_retries, UINT8_MAX); + c->tcp.syn_linear_timeouts = MIN(syn_linear_timeouts, UINT8_MAX); + + debug("TCP SYN parameters: retries=%"PRIu8", linear_timeouts=%"PRIu8, + 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); + 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 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 timeout + * 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