udev: enable kill workers timer when processing queued events stopped

It is not necessary to keep idle workers so long time in that case.

src/udev/udev-manager-ctrl.c

@@ -29,6 +29,7 @@ static int on_ctrl_msg(UdevCtrl *uctrl, UdevCtrlMessageType type, const UdevCtrl
         case UDEV_CTRL_STOP_EXEC_QUEUE:
                 log_debug("Received udev control message (STOP_EXEC_QUEUE)");
                 manager->stop_exec_queue = true;
+                (void) manager_reset_kill_workers_timer(manager);
                 break;
         case UDEV_CTRL_START_EXEC_QUEUE:
                 log_debug("Received udev control message (START_EXEC_QUEUE)");

src/udev/udev-manager.c

@@ -201,7 +201,7 @@ static int on_kill_workers_event(sd_event_source *s, uint64_t usec, void *userda
         return 0;
 }
 
-static int manager_reset_kill_workers_timer(Manager *manager) {
+int manager_reset_kill_workers_timer(Manager *manager) {
         int r;
 
         assert(manager);

src/udev/udev-manager.h

@@ -93,6 +93,7 @@ void manager_exit(Manager *manager);
 void notify_ready(Manager *manager);
 
 void manager_kill_workers(Manager *manager, int signo);
+int manager_reset_kill_workers_timer(Manager *manager);
 
 bool devpath_conflict(const char *a, const char *b);
 

src/udev/udev-varlink.c

@@ -136,6 +136,14 @@ static int vl_method_start_stop_exec_queue(sd_varlink *link, sd_json_variant *pa
 
         log_debug("Received %s()", method);
         manager->stop_exec_queue = streq(method, "io.systemd.Udev.StopExecQueue");
+
+        /* In case that processing queued events will be stopped for a while, regardless if there exist
+         * queued events, enable the kill workers timer here unless it is already enabled. Note, it is not
+         * necessary to disable the timer when processing is restarted, as it will be anyway disabled in
+         * on_post() -> event_queue_start(). */
+        if (manager->stop_exec_queue)
+                (void) manager_reset_kill_workers_timer(manager);
+
         return sd_varlink_reply(link, NULL);
 }