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[184.144.111.238]) by smtp.gmail.com with ESMTPSA id t12sm2348773ioc.11.2021.06.29.09.51.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Jun 2021 09:51:18 -0700 (PDT) Date: Tue, 29 Jun 2021 12:51:17 -0400 From: Peter Xu To: Leonardo Bras Subject: Re: [PATCH v2 1/1] migration: Unregister yank if migration setup fails Message-ID: References: <20210629050522.147057-1-leobras@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210629050522.147057-1-leobras@redhat.com> 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 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=-0.435, 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, Lukas Straub , "Dr. David Alan Gilbert" , Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jun 29, 2021 at 02:05:23AM -0300, Leonardo Bras wrote: > Currently, if a qemu instance is started with "-incoming defer" and > an incorect parameter is passed to "migrate_incoming", it will print the > expected error and reply with "duplicate yank instance" for any upcoming > "migrate_incoming" command. > > This renders current qemu process unusable, and requires a new qemu > process to be started before accepting a migration. > > This is caused by a yank_register_instance() that happens in > qemu_start_incoming_migration() but is never reverted if any error > happens. > > Solves this by unregistering the instance if anything goes wrong > in the function, allowing a new "migrate_incoming" command to be > accepted. > > Fixes: b5eea99ec2f ("migration: Add yank feature", 2021-01-13) > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1974366 > Signed-off-by: Leonardo Bras > Reviewed-by: Peter Xu > > --- > Changes since v1: > - Add ERRP_GUARD() at the beginning of the function, so it deals with > errp passed as NULL, and does correct error propagation. > --- > migration/migration.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/migration/migration.c b/migration/migration.c > index 4228635d18..af0c72609f 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -454,6 +454,7 @@ void migrate_add_address(SocketAddress *address) > > static void qemu_start_incoming_migration(const char *uri, Error **errp) > { > + ERRP_GUARD(); > const char *p = NULL; > > if (!yank_register_instance(MIGRATION_YANK_INSTANCE, errp)) { > @@ -474,9 +475,13 @@ static void qemu_start_incoming_migration(const char *uri, Error **errp) > } else if (strstart(uri, "fd:", &p)) { > fd_start_incoming_migration(p, errp); > } else { > - yank_unregister_instance(MIGRATION_YANK_INSTANCE); > error_setg(errp, "unknown migration protocol: %s", uri); > } > + > + if (*errp) { > + yank_unregister_instance(MIGRATION_YANK_INSTANCE); > + } > + > } > > static void process_incoming_migration_bh(void *opaque) > -- Leo, The patch looks great to me, thanks. Though I found that maybe we need to fix it in another way due to some other reason out of scope of this issue. The problem is today I encountered another yank crashing qemu when trying to do postcopy recover twice. The problem here is both initial incoming migration and postcopy recovery uses qemu_start_incoming_migration(), while in qmp_migrate_recover() b5eea99ec2f5c calls unregister before calling qemu_start_incoming_migration(). I believe it wanted to mitigate the next call to yank_register_instance() to make it work, but I think that's wrong... Firstly, if during recover, we should keep the yank instance there, not "quickly removing and adding it back". Meanwhile, as I mentioned calling qmp_migrate_recover() twice with b5eea99ec2f5c will directly crash the dest qemu because the 1st call of qmp_migrate_recover() will unregister permanently when channel failed to establish, then the 2nd call of qmp_migrate_recover() crashes at yank_unregister_instance(). I'll post an alternative fix of this issue (plus another postcopy recovery fix) to show better on what I meant. Thanks, -- Peter Xu