[PATCH] list: add missing empty list check to list_cut_before()

[Ziran Zhang <zhangcoder@yeah.net>]

list_cut_before() lacks the list_empty() guard present
in list_cut_position().

With an empty head and an entry not on the list, it
corrupts the list.

Add the missing check.  When head is empty, initialize
@list as empty, consistent with the existing
head->next == entry case.

Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
---
 include/linux/list.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/list.h b/include/linux/list.h
index 77fb62f79928..4d2061d35beb 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -555,6 +555,11 @@ static inline void list_cut_before(struct list_head *list,
 				   struct list_head *head,
 				   struct list_head *entry)
 {
+	if (list_empty(head)) {
+		INIT_LIST_HEAD(list);
+		return;
+	}
+
 	if (head->next == entry) {
 		INIT_LIST_HEAD(list);
 		return;
-- 
2.51.0