From 3182fe922bfe643b496950feb9e037d237125954 Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Mon, 29 Dec 2003 05:52:48 -0800 Subject: [PATCH] [PATCH] list_empty_careful() documentation. From: Ingo Molnar I'd also suggest the following patch below, to clarify the use of unsynchronized list_empty(). list_empty_careful() can only be safe in the very specific case of "one-shot" list entries which might be removed by another CPU. (but nothing else can happen to them and this is their only final state.) list_empty_careful() is otherwise completely unsynchronized on both the compiler and CPU level and is not 'SMP safe' in any way. --- include/linux/list.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/list.h b/include/linux/list.h index 0835011b0ffbd..9a5df31af22e6 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -212,6 +212,12 @@ static inline int list_empty(const struct list_head *head) * list_empty_careful - tests whether a list is * empty _and_ checks that no other CPU might be * in the process of still modifying either member + * + * NOTE: using list_empty_careful() without synchronization + * can only be safe if the only activity that can happen + * to the list entry is list_del_init(). Eg. it cannot be used + * if another CPU could re-list_add() it. + * * @head: the list to test. */ static inline int list_empty_careful(const struct list_head *head) -- 2.53.0