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=-10.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 BD88AC47089 for ; Thu, 27 May 2021 13:54:22 +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 3BA55613C5 for ; Thu, 27 May 2021 13:54:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3BA55613C5 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]:55182 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lmGSr-0008PS-GT for qemu-devel@archiver.kernel.org; Thu, 27 May 2021 09:54:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47974) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lmG9r-0005Kb-4R for qemu-devel@nongnu.org; Thu, 27 May 2021 09:34:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:33265) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lmG9k-0000xR-Uh for qemu-devel@nongnu.org; Thu, 27 May 2021 09:34:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622122475; 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=sJwhFnaU5J7/FAXguAsMg59v6E29k+H9JsfC0Rhw3zY=; b=cSu0R7QbWL4bFwdSCD+ZYCSXZVFecqRRqkaidCXrlff3spR93aTVUpK5s/PVhPKhhbyOmD ycgyMphqIAMVP0JgrmTnHvX11WUSwg7LzUt42rQQH46eouvemrdaAo8vEyl+we4MKZS9t2 IKqYTFGHM6bGUxxzT6whM7GtdlxSt3w= 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-520-GmfrnF5eNTu74JCrhPYJkA-1; Thu, 27 May 2021 09:34:30 -0400 X-MC-Unique: GmfrnF5eNTu74JCrhPYJkA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B6E2F803624; Thu, 27 May 2021 13:34:29 +0000 (UTC) Received: from work-vm (ovpn-114-249.ams2.redhat.com [10.36.114.249]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8473960864; Thu, 27 May 2021 13:34:25 +0000 (UTC) Date: Thu, 27 May 2021 14:34:23 +0100 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH 1/1] yank: Unregister function when using TLS migration Message-ID: References: <20210526200540.1088333-1-leobras.c@gmail.com> <20210526232103.39e2a7d0@gecko.fritz.box> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.374, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Leonardo Bras , Lukas Straub , qemu-devel@nongnu.org, Peter Xu , Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Daniel P. Berrangé (berrange@redhat.com) wrote: > On Thu, May 27, 2021 at 09:09:09AM -0400, Peter Xu wrote: > > On Thu, May 27, 2021 at 01:37:42PM +0100, Daniel P. Berrangé wrote: > > > On Thu, May 27, 2021 at 08:23:52AM -0400, Peter Xu wrote: > > > > On Thu, May 27, 2021 at 09:46:54AM +0100, Daniel P. Berrangé wrote: > > > > > On Wed, May 26, 2021 at 05:58:58PM -0400, Peter Xu wrote: > > > > > > On Wed, May 26, 2021 at 11:21:03PM +0200, Lukas Straub wrote: > > > > > > > On Wed, 26 May 2021 16:40:35 -0400 > > > > > > > Peter Xu wrote: > > > > > > > > > > > > > > > On Wed, May 26, 2021 at 05:05:40PM -0300, Leonardo Bras wrote: > > > > > > > > > After yank feature was introduced, whenever migration is started using TLS, > > > > > > > > > the following error happens in both source and destination hosts: > > > > > > > > > > > > > > > > > > (qemu) qemu-kvm: ../util/yank.c:107: yank_unregister_instance: > > > > > > > > > Assertion `QLIST_EMPTY(&entry->yankfns)' failed. > > > > > > > > > > > > > > > > > > This happens because of a missing yank_unregister_function() when using > > > > > > > > > qio-channel-tls. > > > > > > > > > > > > > > > > > > Fix this by also allowing TYPE_QIO_CHANNEL_TLS object type to perform > > > > > > > > > yank_unregister_function() in channel_close() and multifd_load_cleanup(). > > > > > > > > > > > > > > > > > > Fixes: 50186051f ("Introduce yank feature") > > > > > > > > > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1964326 > > > > > > > > > Signed-off-by: Leonardo Bras > > > > > > > > > > > > > > > > Leo, > > > > > > > > > > > > > > > > Thanks for looking into it! > > > > > > > > > > > > > > > > So before looking int the fix... I do have a doubt on why we only enable yank > > > > > > > > on socket typed, as I think tls should also work with qio_channel_shutdown(). > > > > > > > > > > > > > > > > IIUC the confused thing here is we register only for qio-socket, however tls > > > > > > > > will actually call migration_channel_connect() twice, first with a qio-socket, > > > > > > > > then with the real tls-socket. For tls I feel like we have registered with the > > > > > > > > wrong channel - instead of the wrapper socket ioc, we should register to the > > > > > > > > final tls ioc? > > > > > > > > > > > > > > > > Lukas, is there a reason? > > > > > > > > > > > > > > > > > > > > > > Hi, > > > > > > > There is no specific reason. Both ways work equally well in preventing > > > > > > > qemu from hanging. shutdown() for tls-channel just makes it abort a > > > > > > > little sooner (by not attempting to encrypt and send data anymore). > > > > > > > > > > > > > > I don't lean either way. I guess registering it on the tls-channel > > > > > > > makes is a bit more explicit and clearer. > > > > > > > > > > > > Agreed, because IMHO logically the migration code should not be aware of > > > > > > internals of IOChannels, e.g., we shouldn't need to know ioc->master is the > > > > > > socket ioc of tls ioc to unregister. > > > > > > > > > > I think it is atually better to ignore the TLS channel and *always* yank > > > > > on the undering socket IO channel. The yank functionality is intended to > > > > > be used in a scenario where we know the channels are broken. If yank > > > > > calls the high level IO channel it is potentially going to try to do a > > > > > cleanup shutdown that we know will fail because of the broken network. > > > > > > > > Could you elaborate what's the "cleanup shutdown"? > > > > > > > > The yank calls migration_yank_iochannel: > > > > > > > > void migration_yank_iochannel(void *opaque) > > > > { > > > > QIOChannel *ioc = QIO_CHANNEL(opaque); > > > > > > > > qio_channel_shutdown(ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL); > > > > } > > > > > > > > Where qio_channel_shutdown for tls is nothing but delivers that to the master > > > > channel: > > > > > > > > static int qio_channel_tls_shutdown(QIOChannel *ioc, > > > > QIOChannelShutdown how, > > > > Error **errp) > > > > { > > > > QIOChannelTLS *tioc = QIO_CHANNEL_TLS(ioc); > > > > > > > > qatomic_or(&tioc->shutdown, how); > > > > > > > > return qio_channel_shutdown(tioc->master, how, errp); > > > > } > > > > > > > > So I thought it was a nice wrapper just for things like this, and I didn't see > > > > anything it does more than the io_shutdown for the socket channel. Did I miss > > > > something? > > > > > > Today thats the case, but don't assume it will be the case forever. > > > There is a mechanism in TLS for doing clean shutdown which we've > > > debated including. > > > > > > In general apps *can* just call the shutdown method on the QIOChannelTLS > > > object no matter what. Yank is just a little bit special because of its > > > need to be guaranteed to work even when the network is dead. So yank > > > should always directly call the low level QIOChannelSocket, so thre is > > > a strong guarantee it can't block on something. > > > > Hmm, I am still not fully convinced that that's a valid reason the migration > > code should be aware of how the socket is managed in tls channels... > > > > Does that sound more like a good reason to introduce QIOChannelShutdown with > > QIO_CHANNEL_SHUTDOWN_FORCE so it'll always not block if FORCE set? Then we can > > switch the yank function to use that. > > > > What do you think? > > I think that's unneccessary - the migration code already does similar > things elsewhere when it wants to distinguish TLS usage, so this is not > anything new conceptually. I'd probably agree with Peter here that it would be preferential for the migration code not to know; what we want to do here is give the channel the opportunity to do a hard shutdown, and let the channel worry about it whether it can do that. If you look at the nbd code, it's yank registration calls qio_channel_shutdown on whatever channel it happens to have; so that's probably wrong since I think you're saying that could block. Dave > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK