diff --git a/kernel/kthread.c b/kernel/kthread.c
index 99a3808d086f..39511dd2abc9 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1599,6 +1599,7 @@ void kthread_use_mm(struct mm_struct *mm)
 
 	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
 	WARN_ON_ONCE(tsk->mm);
+	WARN_ON_ONCE(!mm->user_ns);
 
 	/*
 	 * It is possible for mm to be the same as tsk->active_mm, but