fix llist_for_each_entry*

enabling more of __notify_execute_cb() and running the intel xorg driver
on broadwell would fault in __notify_execute_cb() on
movq 0x38(%rsi),%r12

offsetof(struct execute_cb, work.node.llist) 0x38

llist_entry(NULL must not return NULL, it needs to wrap around
and return NULL minus the offset

the iterators stop when the offset added back to the result of
llist_entry() is NULL

they test that the first node is not NULL or that the next pointer
stored in a previous iteration of the loop is not NULL

1 files changed, 3 insertions, 4 deletions

diff --git a/sys/dev/pci/drm/include/linux/llist.h b/sys/dev/pci/drm/include/linux/llist.h
index 8c0b37da123..2e518eb5941 100644
--- a/sys/dev/pci/drm/include/linux/llist.h
+++ b/sys/dev/pci/drm/include/linux/llist.h
@@ -13,8 +13,7 @@ struct llist_head {
 	struct llist_node *first;
 };
 
-#define llist_entry(ptr, type, member) \
-	((ptr) ? container_of(ptr, type, member) : NULL)
+#define llist_entry(ptr, type, member)	container_of(ptr, type, member)
 
 static inline struct llist_node *
 llist_del_all(struct llist_head *head)
@@ -82,13 +81,13 @@ llist_empty(struct llist_head *head)
 
 #define llist_for_each_entry_safe(pos, n, node, member) 		\
 	for (pos = llist_entry((node), __typeof(*pos), member); 	\
-	    pos != NULL &&						\
+	    ((char *)(pos) + offsetof(typeof(*(pos)), member)) != NULL && \
 	    (n = llist_entry(pos->member.next, __typeof(*pos), member), pos); \
 	    pos = n)
 
 #define llist_for_each_entry(pos, node, member)				\
 	for ((pos) = llist_entry((node), __typeof(*(pos)), member);	\
-	    (pos) != NULL;						\
+	    ((char *)(pos) + offsetof(typeof(*(pos)), member)) != NULL;	\
 	    (pos) = llist_entry((pos)->member.next, __typeof(*(pos)), member))
 
 #endif