homed: make sure our worker processes finish before we exit

When exiting, let's explicitly wait for our worker processes to finish
first. That's useful if unmounting of /home/ is scheduled to happen
right after homed is down, as we then can be sure that the home
directories are properly unmounted and detached by the time homed is
fully terminated (otherwise it might happen that our worker gets killed
by the service manager, thus leaving the home directory and its backing
devices up/left for auto-clean which might be async).

Likely fixes #16842

src/home/homed-home.c

@@ -2739,6 +2739,19 @@ int home_set_current_message(Home *h, sd_bus_message *m) {
         return 1;
 }
 
+int home_wait_for_worker(Home *h) {
+        assert(h);
+
+        if (h->worker_pid <= 0)
+                return 0;
+
+        log_info("Worker process for home %s is still running while exiting. Waiting for it to finish.", h->user_name);
+        (void) wait_for_terminate(h->worker_pid, NULL);
+        (void) hashmap_remove_value(h->manager->homes_by_worker_pid, PID_TO_PTR(h->worker_pid), h);
+        h->worker_pid = 0;
+        return 1;
+}
+
 static const char* const home_state_table[_HOME_STATE_MAX] = {
         [HOME_UNFIXATED]                   = "unfixated",
         [HOME_ABSENT]                      = "absent",

src/home/homed-home.h

@@ -165,5 +165,7 @@ int home_auto_login(Home *h, char ***ret_seats);
 
 int home_set_current_message(Home *h, sd_bus_message *m);
 
+int home_wait_for_worker(Home *h);
+
 const char *home_state_to_string(HomeState state);
 HomeState home_state_from_string(const char *s);

src/home/homed-manager.c

@@ -232,8 +232,13 @@ int manager_new(Manager **ret) {
 }
 
 Manager* manager_free(Manager *m) {
+        Home *h;
+
         assert(m);
 
+        HASHMAP_FOREACH(h, m->homes_by_worker_pid)
+                (void) home_wait_for_worker(h);
+
         hashmap_free(m->homes_by_uid);
         hashmap_free(m->homes_by_name);
         hashmap_free(m->homes_by_worker_pid);