spapr: Don't request to unplug the same core twice

We must not call spapr_drc_detach() on a detached DRC otherwise bad things
can happen, ie. QEMU hangs or crashes. This is easily demonstrated with
a CPU hotplug/unplug loop using QMP.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <157185826035.3073024.1664101000438499392.stgit@bahia.lan>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
1 file changed