Fix subtle bug in "finish_wait()", which can cause kernel stack

corruption on SMP because of another CPU still accessing a waitqueue
even after it was de-allocated.

Use a careful version of the list emptiness check to make sure we
don't de-allocate the stack frame before the waitqueue is all done.

1 files changed, 12 insertions, 0 deletions

diff --git a/include/linux/list.h b/include/linux/list.h
index b7d383e6a312..0835011b0ffb 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -208,6 +208,18 @@ static inline int list_empty(const struct list_head *head)
 	return head->next == 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
+ * @head: the list to test.
+ */
+static inline int list_empty_careful(const struct list_head *head)
+{
+	struct list_head *next = head->next;
+	return (next == head) && (next == head->prev);
+}
+
 static inline void __list_splice(struct list_head *list,
 				 struct list_head *head)
 {