uffd: add config to disable fetch memory data in the background

Signed-off-by: Liu Hua <[email protected]>

criu/cr-restore.c

@@ -116,6 +116,7 @@
 #endif
 
 struct pstree_item *current;
+static bool disable_background_lazy_page_fetch;
 
 static int restore_task_with_children(void *);
 static int sigreturn_restore(pid_t pid, struct task_restore_args *ta, unsigned long alen, CoreEntry *core);
@@ -2213,7 +2214,7 @@ static int restore_root_task(struct pstree_item *init)
 		goto out_kill_network_unlocked;
 	}
 
-	if (lazy_pages_finish_restore())
+	if (!disable_background_lazy_page_fetch && lazy_pages_finish_restore())
 		goto out_kill_network_unlocked;
 
 	__restore_switch_stage(CR_STATE_COMPLETE);
@@ -3499,3 +3500,8 @@ static int sigreturn_restore(pid_t pid, struct task_restore_args *task_args, uns
 	exit(1);
 	return -1;
 }
+
+static void __attribute__((constructor)) pagemap_cache_init(void)
+{
+    disable_background_lazy_page_fetch = (getenv("CRIU_DISABLE_BACKGROUND_LAZY_PAGE_FETCH") != NULL);
+}