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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 D2AB8C43331 for ; Fri, 27 Mar 2020 18:47:09 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9A7C4206F2 for ; Fri, 27 Mar 2020 18:47:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RNfwilxM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9A7C4206F2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45718 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jHu0a-0001ZQ-QR for qemu-devel@archiver.kernel.org; Fri, 27 Mar 2020 14:47:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:46321) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jHtzk-00015D-1d for qemu-devel@nongnu.org; Fri, 27 Mar 2020 14:46:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jHtzh-00015R-T0 for qemu-devel@nongnu.org; Fri, 27 Mar 2020 14:46:15 -0400 Received: from us-smtp-delivery-74.mimecast.com ([216.205.24.74]:44567) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jHtzh-00014P-Px for qemu-devel@nongnu.org; Fri, 27 Mar 2020 14:46:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585334773; 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=zNgJp/0TCcNGo2/Wqzdmm1HrnxglrLazcI0u1oqXC+8=; b=RNfwilxMfeTTO0uxL3r3RO8twbkejrfue+Kl4dFZ2Ul4J7VFaT5zG5v1I1jNjPimU1Ckvh sxoLwgjYifyh8n8dplR3VdfX13EwUj8ZM7RdfsJ/FdLkPobKEWGqYIPqw1Hk1qXxdU/p0c 6RBllmni0cE3utQJ3recaVFlOshqMrA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-167-lhfYLjlBMeexBZu4QncbNg-1; Fri, 27 Mar 2020 14:46:04 -0400 X-MC-Unique: lhfYLjlBMeexBZu4QncbNg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 53AD21005513; Fri, 27 Mar 2020 18:46:03 +0000 (UTC) Received: from [10.3.113.103] (ovpn-113-103.phx2.redhat.com [10.3.113.103]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 07B2F1001B28; Fri, 27 Mar 2020 18:46:02 +0000 (UTC) Subject: Re: [PATCH 2/3] io: Support shutdown of TLS channel To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20200327161936.2225989-1-eblake@redhat.com> <20200327161936.2225989-3-eblake@redhat.com> <20200327164040.GQ1619@redhat.com> <20200327174334.GT1619@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <0b3fb119-64c5-0e03-c43d-15e9683fcfd7@redhat.com> Date: Fri, 27 Mar 2020 13:46:02 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200327174334.GT1619@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 216.205.24.74 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/27/20 12:43 PM, Daniel P. Berrang=C3=A9 wrote: >>> I don't think it is acceptable to do this loop here. The gnutls_bye() >>> function triggers several I/O operations which could block. Looping >>> like this means we busy-wait, blocking this thread for as long as I/O >>> is blocking on the socket. >> >> Hmm, good point. Should we give qio_channel_tls_shutdown a bool paramet= er >> that says whether it should wait (good for use when we are being run in = a >> coroutine and can deal with the additional I/O) or just fail with -EAGAI= N >> (which the caller can ignore if it is not worried)? >=20 > A bool would not be sufficient, because the caller would need to know > which direction to wait for I/O on. >=20 > Looking at the code it does a flush of outstanding data, then sends > some bytes, and then receives some bytes. The write will probably > work most of the time, but the receive is almost always going to > return -EAGAIN. So I don't think that failing with EGAIN is going > to be much of a benefit. Here, I'm guessing you're talking about gnutls lib/record.c. But note:=20 for GNUTLS_SHUT_WR, it only does _gnutls_io_write_flush and=20 gnutls_alert_send; the use of _gnutls_recv_int is reserved for=20 GNUTLS_SHUT_RDWR. When informing the other end that you are not going=20 to write any more, you don't have to wait for a reply. >=20 >>> If we must call gnutls_bye(), then it needs to be done in a way that >>> can integrate with the main loop so it poll()'s / unblocks the current >>> coroutine/thread. This makes the whole thing significantly more >>> complex to deal with, especially if the shutdown is being done in >>> cleanup paths which ordinarily are expected to execute without >>> blocking on I/O. This is the big reason why i never made any attempt >>> to use gnutls_bye(). >> >> We _are_ using gnutls_bye(GNUTLS_SHUT_RDWR) on the close() path (which i= s >=20 > Are you sure ? AFAIK there is no existing usage of gnutls_bye() at all > in QEMU. Oh, I'm confusing that with nbdkit, which does use=20 gnutls_bye(GNUTLS_SHUT_RDWR) but does not wait for a response (at least,=20 not yet). >=20 >> indeed a cleanup path where not blocking is worthwhile) even without thi= s >> patch, but the question is whether using gnutls_bye(GNUTLS_SHUT_WR) in t= he >> normal data path, where we are already using coroutines to manage callba= cks, >> can benefit the remote endpoint, giving them a chance to see clean shutd= own >> instead of abrupt termination. >=20 > I'm not convinced the clean shutdown at the TLS level does anything impor= tant > given that we already have done a clean shutdown at the NBD level. Okay, then for now, I'll still try and see if I can fix the=20 libnbd/nbdkit hang without relying on qemu sending a clean=20 gnutls_bye(GNUTLS_SHUT_WR). --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org