machined: only Unref units that we AddRef'd

b92d0b4c5adef37e9de8f6cc22a0e27b97fcf3ad added AddRef to the StartTransientUnit
call in machine_start_scope()/manager_start_scope() and a corresponding Unref
call in machine_stop_scope(). But when we are running systemd-nspawn@ with
--keep unit, the unit is not created by machined so the AddRef never happens.
Then when trying to stop the unit, we'd get:

systemd-machined[1101]: Sent message type=method_call sender=n/a destination=org.freedesktop.systemd1 path=/org/freedesktop/systemd1 interface=org.freedesktop.systemd1.Manager member=UnrefUnit cookie=37 reply_cookie=0 signature=s error-name=n/a error-message=n/a
systemd-machined[1101]: Got message type=error sender=:1.1 destination=:1.13 path=n/a interface=n/a member=n/a cookie=2443 reply_cookie=37 signature=s error-name=org.freedesktop.systemd1.NotReferenced error-message=Unit has not been referenced yet.
systemd-machined[1101]: Failed to drop reference to machine scope, ignoring: Unit has not been referenced yet.

2 files changed, 8 insertions, 3 deletions

diff --git a/src/machine/machine.c b/src/machine/machine.c
index b5d017a671..c6475a5398 100644
--- a/src/machine/machine.c
+++ b/src/machine/machine.c
@@ -355,6 +355,7 @@ static int machine_start_scope(Machine *m, sd_bus_message *properties, sd_bus_er
                         return log_error_errno(r, "Failed to start machine scope: %s", bus_error_message(error, r));
 
                 m->unit = TAKE_PTR(scope);
+                m->referenced = true;
                 free_and_replace(m->scope_job, job);
         }
 
@@ -422,9 +423,12 @@ static int machine_stop_scope(Machine *m) {
         } else
                 free_and_replace(m->scope_job, job);
 
-        q = manager_unref_unit(m->manager, m->unit, &error);
-        if (q < 0)
-                log_warning_errno(q, "Failed to drop reference to machine scope, ignoring: %s", bus_error_message(&error, r));
+        if (m->referenced) {
+                q = manager_unref_unit(m->manager, m->unit, &error);
+                if (q < 0)
+                        log_warning_errno(q, "Failed to drop reference to machine scope, ignoring: %s", bus_error_message(&error, r));
+                m->referenced = false;
+        }
 
         return r;
 }
diff --git a/src/machine/machine.h b/src/machine/machine.h
index f7471be8f5..0a39e61052 100644
--- a/src/machine/machine.h
+++ b/src/machine/machine.h
@@ -54,6 +54,7 @@ struct Machine {
         bool in_gc_queue:1;
         bool started:1;
         bool stopping:1;
+        bool referenced:1;
 
         sd_bus_message *create_message;