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 X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS 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 8485EC43381 for ; Fri, 22 Feb 2019 15:11:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5534720657 for ; Fri, 22 Feb 2019 15:11:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="C2DByZwa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726380AbfBVPLR (ORCPT ); Fri, 22 Feb 2019 10:11:17 -0500 Received: from mail-ua1-f68.google.com ([209.85.222.68]:37888 "EHLO mail-ua1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726325AbfBVPLR (ORCPT ); Fri, 22 Feb 2019 10:11:17 -0500 Received: by mail-ua1-f68.google.com with SMTP id p9so2237550uaa.5 for ; Fri, 22 Feb 2019 07:11:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=M3Ro7AG/5w3ilJ8C2EhLesq53D/y9X5HjCZjTquiytQ=; b=C2DByZwaXDLglmC+AL36i3WGjxjPXFKzYk1rdpnJrsS1Ylg/w+RO+48rO90xisx8jx Z2naKztF0hYizjs2EYUQquN/jD6OX/ynzh2sGh9b8WC0xIBOVWh1jhbGc+i/lEjpB2v5 hVtt/FrqJth8esFB8k9dR+GneO1jUc85WOtbiQlPgVYLLPMqYnxQcb1xotua3ChWRqlp xbZ0x5bCHdvprXWffXmCa6GV4HRFcZ4w4Gbs8HnIYJduY+HozpUH2lw04QeYt48k7LyW OAN2Jvl8Aez0sEyLuS2LB2V+wVqXSwGPWyegI0+4xyTZ4G45TTWWhsiTVEaESsgI8IM7 FaAg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=M3Ro7AG/5w3ilJ8C2EhLesq53D/y9X5HjCZjTquiytQ=; b=aAKJywyg8cia+AE/TgaAxGqDI7SIHLdqDsQTlUvPsPlQwyuSSBfRLB0aKkr2U+niZi bQQUimncuNXwD32aSTcOFW/jLh7lB2nAACdSgVQJSEFVJbyr2DNZwXJeomWN8ieebXBw XJRTlK+rhmJcSZjOO/uw5ZYVJBxrGQSFJ870qv7QZMoUJUtm5i5L8AUBgvuFWU1DsUR3 umi4VqQN6UFWR0rXY3NuNFW6IjdFPaBzEcwg+4vJ2Mo6Svc93X7v/Mmpm4l7AL8zBFxh +x8OtbFzWWEApd1RCwjgVIlUtdzF60pjTseEL8VPqD5zMfBvXBr1MlDE3MLShUvP89g4 ZJUw== X-Gm-Message-State: AHQUAuYYfG+kXetDn7aNk/Ce5vBY1qbX9HiK7ZTyZYx+QRs5q3c2rfS0 XK6XzYgai9MQcRJKyChFn78N7YmiG+AbIc/cZpo= X-Google-Smtp-Source: AHgI3IZv3fdlMHWyVmrTOk2gP6wLxdeHVjtXOQMdq1BN+967PrVmSFOdd3kQhmkvhU64e7gr9JUg/OiPt5rsYwoRiEI= X-Received: by 2002:a05:6102:18f:: with SMTP id r15mr2364415vsq.215.1550848275898; Fri, 22 Feb 2019 07:11:15 -0800 (PST) MIME-Version: 1.0 References: <20190220145650.21566-1-olga.kornievskaia@gmail.com> <1550837576.6456.3.camel@redhat.com> <05e439b3c419f3ac173feb770d3d2ae1d7500a2d.camel@hammerspace.com> In-Reply-To: <05e439b3c419f3ac173feb770d3d2ae1d7500a2d.camel@hammerspace.com> From: Olga Kornievskaia Date: Fri, 22 Feb 2019 10:11:04 -0500 Message-ID: Subject: Re: [PATCH 1/1] SUNRPC: fix handling of half-closed connection To: Trond Myklebust Cc: "anna.schumaker@netapp.com" , "linux-nfs@vger.kernel.org" , "dwysocha@redhat.com" Content-Type: text/plain; charset="UTF-8" Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Fri, Feb 22, 2019 at 10:06 AM Trond Myklebust wrote: > > On Fri, 2019-02-22 at 09:46 -0500, Olga Kornievskaia wrote: > > On Fri, Feb 22, 2019 at 8:45 AM Trond Myklebust < > > trondmy@hammerspace.com> wrote: > > > On Fri, 2019-02-22 at 07:12 -0500, Dave Wysochanski wrote: > > > > Hi Olga, > > > > > > > > Do you have a reproducer for this? A number of months ago I did > > > > a > > > > significant amount of testing with half-closed connections, after > > > > we > > > > had reports of connections stuck in FIN_WAIT2 in some older > > > > kernels. > > > > What I found was with kernels that had the tcp keepalives (commit > > > > 7f260e8575bf53b93b77978c1e39f8e67612759c), I could only reproduce > > > > a > > > > hang of a few minutes, after which time the tcp keepalive code > > > > would > > > > reset the connection. > > > > > > > > That said it was a while ago and something subtle may have > > > > changed. > > > > Also I'm not not sure if your header implies an indefinite hang > > > > or > > > > just > > > > a few minutes. > > > > > > > > Thanks. > > > > > > > > > > > > On Wed, 2019-02-20 at 09:56 -0500, Olga Kornievskaia wrote: > > > > > From: Olga Kornievskaia > > > > > > > > > > When server replies with an ACK to client's FIN/ACK, client > > > > > ends > > > > > up stuck in a TCP_FIN_WAIT2 state and client's mount hangs. > > > > > Instead, make sure to close and reset client's socket and > > > > > transport > > > > > when transitioned into that state. > > > > Hi Trond, > > > > > So, please do note that we do not want to ignore the FIN_WAIT2 > > > state > > > > But we do ignore the FIN_WAIT2 state. > > We do not. We wait for the server to send a FIN, which is precisely the > reason for which FIN_WAIT2 exists. > > > > > > because it implies that the server has not closed the socket on its > > > side. > > > > That's correct. > > > > > That again means that we cannot re-establish a connection using > > > the same source IP+port to the server, which is problematic for > > > protocols such as NFSv3 which rely on standard duplicate reply > > > cache > > > for correct replay semantics. > > > > that's exactly what's happening that a client is unable to establish > > a > > new connection to the server. With the patch, the client does an RST > > and it re-uses the port and all is well for NFSv3. > > RST is not guaranteed to be delivered to the recipient. That's why the > TCP protocol defines FIN: it is a guaranteed to be delivered because it > is ACKed. > > > > This is why we don't just set the TCP_LINGER2 socket option and > > > call > > > sock_release(). The choice to try to wait it out is deliberate > > > because > > > the alternative is that we end up with busy-waiting re-connection > > > attempts. > > > > Why would it busy-wait? In my testing, RST happens and new connection > > is established? > > Only if the server has dropped the connection without notifying the > client. Yes the server dropped the connection without notifying the client (or perhaps something in the middle did it as an attack). Again, I raise this concern for the sake of dealing with this as an attack. I have no intentions of catering to broken servers. If this is not a possible attack, then we don't have to deal with it.