6e9beed308
block-nbd was refacted during release 6.2.0, but we didn't induced all the needed patches within the 6.2.0 baseline, which leads to vm crash during migration. the reasons are as below: when iothread is configured, the coroutines should get back to the exact iothread that was out of. But within the 6.2.0 baseline, patches were missing, nbd related coroutine didn't have its related aio_context. It in fact get to the mainline aio_context, the mistaken context leads to vm crash.