restore: Normalize first and last staging switches

Don't set futexes by hands, use the restore_switch_stage
helpers explicitly (for code readability).
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/cr-restore.c

@@ -1592,10 +1592,18 @@ static int restore_wait_inprogress_tasks()
 	return 0;
 }
 
-static void __restore_switch_stage(int next_stage)
+static inline void __restore_switch_stage_nw(int next_stage)
 {
 	futex_set(&task_entries->nr_in_progress,
 			stage_participants(next_stage));
+	futex_set(&task_entries->start, next_stage);
+}
+
+static inline void __restore_switch_stage(int next_stage)
+{
+	if (next_stage != CR_STATE_COMPLETE)
+		futex_set(&task_entries->nr_in_progress,
+				stage_participants(next_stage));
 	futex_set_and_wake(&task_entries->start, next_stage);
 }
 
@@ -1893,8 +1901,7 @@ static int restore_root_task(struct pstree_item *init)
 	if (prepare_namespace_before_tasks())
 		return -1;
 
-	futex_set(&task_entries->nr_in_progress,
-			stage_participants(CR_STATE_RESTORE_NS));
+	__restore_switch_stage_nw(CR_STATE_RESTORE_NS);
 
 	ret = fork_with_pid(init);
 	if (ret < 0)
@@ -2051,7 +2058,7 @@ static int restore_root_task(struct pstree_item *init)
 	ret = catch_tasks(root_seized, &flag);
 
 	pr_info("Restore finished successfully. Resuming tasks.\n");
-	futex_set_and_wake(&task_entries->start, CR_STATE_COMPLETE);
+	__restore_switch_stage(CR_STATE_COMPLETE);
 
 	if (ret == 0)
 		ret = compel_stop_on_syscall(task_entries->nr_threads,
@@ -2130,7 +2137,7 @@ static int prepare_task_entries(void)
 	task_entries->nr_threads = 0;
 	task_entries->nr_tasks = 0;
 	task_entries->nr_helpers = 0;
-	futex_set(&task_entries->start, CR_STATE_RESTORE_NS);
+	futex_set(&task_entries->start, CR_STATE_FAIL);
 	mutex_init(&task_entries->userns_sync_lock);
 
 	return 0;