migration/tls: add error handling in multifd_tls_handshake_thread

If any error happens during multifd send thread creating (e.g. channel broke
because new domain is destroyed by the dst), multifd_tls_handshake_thread
may exit silently, leaving main migration thread hanging (ram_save_setup ->
multifd_send_sync_main -> qemu_sem_wait(&p->sem_sync)).
Fix that by adding error handling in multifd_tls_handshake_thread.

Signed-off-by: Hao Wang <wanghao232@huawei.com>
Message-Id: <20210209104237.2250941-3-wanghao232@huawei.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Chuan Zheng <zhengchuan@huawei.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/multifd.c

@@ -739,7 +739,16 @@ static void multifd_tls_outgoing_handshake(QIOTask *task,
     } else {
         trace_multifd_tls_outgoing_handshake_complete(ioc);
     }
-    multifd_channel_connect(p, ioc, err);
+
+    if (!multifd_channel_connect(p, ioc, err)) {
+        /*
+         * Error happen, mark multifd_send_thread status as 'quit' although it
+         * is not created, and then tell who pay attention to me.
+         */
+        p->quit = true;
+        qemu_sem_post(&multifd_send_state->channels_ready);
+        qemu_sem_post(&p->sem_sync);
+    }
 }
 
 static void *multifd_tls_handshake_thread(void *opaque)