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[184.145.4.219]) by smtp.gmail.com with ESMTPSA id y12sm1259259qtv.59.2021.05.27.06.09.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 May 2021 06:09:10 -0700 (PDT) Date: Thu, 27 May 2021 09:09:09 -0400 From: Peter Xu To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@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: qemu-devel@nongnu.org, Leonardo Bras , Lukas Straub , "Dr. David Alan Gilbert" , Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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? -- Peter Xu