nvme: acquire a new subsystem if no valid controllers assigned

drivers/nvme/host/core.c

@@ -2704,6 +2704,8 @@ static void nvme_put_subsystem(struct nvme_subsystem *subsys)
 static struct nvme_subsystem *__nvme_find_get_subsystem(const char *subsysnqn)
 {
  struct nvme_subsystem *subsys;
+ struct nvme_ctrl *ctrl;
+ bool active_ctrls = false;
 
  lockdep_assert_held(&nvme_subsystems_lock);
 
@@ -2721,6 +2723,16 @@ static struct nvme_subsystem *__nvme_find_get_subsystem(const char *subsysnqn)
  list_for_each_entry(subsys, &nvme_subsystems, entry) {
  if (strcmp(subsys->subnqn, subsysnqn))
  continue;
+ if (!list_empty(&subsys->ctrls)) {
+ list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
+ if (!nvme_state_terminal(ctrl)) {
+ active_ctrls = true;
+ break;
+ }
+ }
+ }
+ if (!active_ctrls)
+ continue;
  if (!kref_get_unless_zero(&subsys->ref))
  continue;
  return subsys;