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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3FB8BC71153 for ; Thu, 24 Aug 2023 14:57:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241576AbjHXO5R (ORCPT ); Thu, 24 Aug 2023 10:57:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48290 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241924AbjHXO4v (ORCPT ); Thu, 24 Aug 2023 10:56:51 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4F73919B3 for ; Thu, 24 Aug 2023 07:56:47 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E22A866FB9 for ; Thu, 24 Aug 2023 14:56:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0066AC433C7; Thu, 24 Aug 2023 14:56:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1692889006; bh=HfA+FoqkoIaPuYwDtWcVV3Ra6n4i8UD45yGp329fl5A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kPop4VFvKysZfF2nRLxlr4Oq29BRBvIcuAWxkAEobsCW/xE1dwVU8KRYXtHXZuVWd oY42k+t6as3hC8kGJoX6rGoW8LvYlPn3pohONSTjcndmnnLLmj7W4YU2Red7ffGxYX PvJpTB8zpywDRA026RyWt06mh452UOT0EC8c/vm8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Eric Dumazet , Jason Xing , "David S. Miller" Subject: [PATCH 5.15 121/139] net: fix the RTO timer retransmitting skb every 1ms if linear option is enabled Date: Thu, 24 Aug 2023 16:50:44 +0200 Message-ID: <20230824145028.759343994@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20230824145023.559380953@linuxfoundation.org> References: <20230824145023.559380953@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Jason Xing commit e4dd0d3a2f64b8bd8029ec70f52bdbebd0644408 upstream. In the real workload, I encountered an issue which could cause the RTO timer to retransmit the skb per 1ms with linear option enabled. The amount of lost-retransmitted skbs can go up to 1000+ instantly. The root cause is that if the icsk_rto happens to be zero in the 6th round (which is the TCP_THIN_LINEAR_RETRIES value), then it will always be zero due to the changed calculation method in tcp_retransmit_timer() as follows: icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); Above line could be converted to icsk->icsk_rto = min(0 << 1, TCP_RTO_MAX) = 0 Therefore, the timer expires so quickly without any doubt. I read through the RFC 6298 and found that the RTO value can be rounded up to a certain value, in Linux, say TCP_RTO_MIN as default, which is regarded as the lower bound in this patch as suggested by Eric. Fixes: 36e31b0af587 ("net: TCP thin linear timeouts") Suggested-by: Eric Dumazet Signed-off-by: Jason Xing Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_timer.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -582,7 +582,9 @@ out_reset_timer: tcp_stream_is_thin(tp) && icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { icsk->icsk_backoff = 0; - icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); + icsk->icsk_rto = clamp(__tcp_set_rto(tp), + tcp_rto_min(sk), + TCP_RTO_MAX); } else { /* Use normal (exponential) backoff */ icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);