From patchwork Mon Nov 23 12:22:02 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 332334 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9BEA7C2D0E4 for ; Mon, 23 Nov 2020 12:24:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 373952076E for ; Mon, 23 Nov 2020 12:24:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="1PiycF5o" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729847AbgKWMYp (ORCPT ); Mon, 23 Nov 2020 07:24:45 -0500 Received: from mail.kernel.org ([198.145.29.99]:34362 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729863AbgKWMYp (ORCPT ); Mon, 23 Nov 2020 07:24:45 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EFD992076E; Mon, 23 Nov 2020 12:24:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1606134284; bh=l3o67iad6VP+yL5RBsCEyT4t+/Fh7VsG0Vg7+8pyNzY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1PiycF5ozsbnaynUpNSRiTzg/YNUNWwtxoNHsMS113HF3fFMyM18PQXag4E0cANCO wMLOCmcytLedduQymAEdkEO1wbgAkL25R+kfKMB/bqtmN3PJuUx/ZeiA1iXpdctxPU KtlsL9I/+1edWtG4BKtp9Umfj9KDPokMeqMlwbMY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ryan Sharpelletti , Neal Cardwell , Soheil Hassas Yeganeh , Yuchung Cheng , Jakub Kicinski Subject: [PATCH 4.9 16/47] tcp: only postpone PROBE_RTT if RTT is < current min_rtt estimate Date: Mon, 23 Nov 2020 13:22:02 +0100 Message-Id: <20201123121806.326715558@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201123121805.530891002@linuxfoundation.org> References: <20201123121805.530891002@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Ryan Sharpelletti [ Upstream commit 1b9e2a8c99a5c021041bfb2d512dc3ed92a94ffd ] During loss recovery, retransmitted packets are forced to use TCP timestamps to calculate the RTT samples, which have a millisecond granularity. BBR is designed using a microsecond granularity. As a result, multiple RTT samples could be truncated to the same RTT value during loss recovery. This is problematic, as BBR will not enter PROBE_RTT if the RTT sample is <= the current min_rtt sample, meaning that if there are persistent losses, PROBE_RTT will constantly be pushed off and potentially never re-entered. This patch makes sure that BBR enters PROBE_RTT by checking if RTT sample is < the current min_rtt sample, rather than <=. The Netflix transport/TCP team discovered this bug in the Linux TCP BBR code during lab tests. Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") Signed-off-by: Ryan Sharpelletti Signed-off-by: Neal Cardwell Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: Yuchung Cheng Link: https://lore.kernel.org/r/20201116174412.1433277-1-sharpelletti.kdev@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_bbr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -740,7 +740,7 @@ static void bbr_update_min_rtt(struct so filter_expired = after(tcp_time_stamp, bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ); if (rs->rtt_us >= 0 && - (rs->rtt_us <= bbr->min_rtt_us || filter_expired)) { + (rs->rtt_us < bbr->min_rtt_us || filter_expired)) { bbr->min_rtt_us = rs->rtt_us; bbr->min_rtt_stamp = tcp_time_stamp; }