vmm: skip pending memory sends on worker failure

When a memory-sending worker fails, the migration thread calls
`SendAdditionalConnections::cleanup()`. Cleanup tries to enqueue one
`Disconnect` message per worker, but the bounded channel may still
contain `SendMemoryThreadMessage::Memory` values.

The surviving workers currently call `send_memory_ranges()` for each
such value, even though the migration has already failed. Skip that call
when `worker_error` is set. This consumes the queued values without
processing them and lets cleanup enqueue the `Disconnect` messages.

On-behalf-of: SAP leander.kohler@sap.com
Signed-off-by: Leander Kohler <leander.kohler@cyberus-technology.de>
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

Author: Coffeeri

vmm/src/migration/transport.rs

@@ -727,7 +727,9 @@ impl SendAdditionalConnections {
                 })?;
             match message {
                 SendMemoryThreadMessage::Memory(table) => {
-                    if external_cancel.load(Ordering::Acquire) {
+                    if external_cancel.load(Ordering::Acquire)
+                        || worker_error.load(Ordering::Acquire)
+                    {
                         continue;
                     }