monitor: cleanup detection of qmp_dispatcher_co shutting down

Instead of overloading qmp_dispatcher_co_busy, make the coroutine
pointer NULL.  This will make things break spectacularly if somebody
tries to start a request after monitor_cleanup().

AIO_WAIT_WHILE_UNLOCKED() does not need qatomic_mb_read(), because
the macro contains all the necessary memory barriers.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2 files changed