monitor: use aio_co_reschedule_self()

monitor: use aio_co_reschedule_self()

The aio_co_reschedule_self() API is designed to avoid the race
condition between scheduling the coroutine in another AioContext and
yielding.

The QMP dispatch code uses the open-coded version that appears
susceptible to the race condition at first glance:

  aio_co_schedule(qemu_get_aio_context(), qemu_coroutine_self());
  qemu_coroutine_yield();

The code is actually safe because the iohandler and qemu_aio_context
AioContext run under the Big QEMU Lock. Nevertheless, set a good example
and use aio_co_reschedule_self() so it's obvious that there is no race.

Suggested-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20240206190610.107963-6-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>