LinuxKPI: Add compiler barriers to list_for_each_entry_lockless macro

so this list-traversal primitive may safely run concurrently with the
_rcu list-mutation primitives such as list_add_rcu() as long as the
traversal is guarded by rcu_read_lock().

Do it by reusing the "list_for_each_entry_rcu" macro which does the same.
On Linux it implements some additional lockdep stuff which we skip.

Also move the macro to linux/rculist.h where it resides on Linux.

Reviewed by:	hselasky
Differential revision:	https://reviews.freebsd.org/D30795

(cherry picked from commit c0862b2b1fa91636d308a1a41d8dc370691d656e)

2 files changed, 3 insertions, 2 deletions

diff --git a/sys/compat/linuxkpi/common/include/linux/list.h b/sys/compat/linuxkpi/common/include/linux/list.h
index 93db449a4473..37b5b751d21b 100644
--- a/sys/compat/linuxkpi/common/include/linux/list.h
+++ b/sys/compat/linuxkpi/common/include/linux/list.h
@@ -202,8 +202,6 @@ list_del_init(struct list_head *entry)
 	for (p = list_entry((h)->next, typeof(*p), field); &(p)->field != (h); \
 	    p = list_entry((p)->field.next, typeof(*p), field))
 
-#define list_for_each_entry_lockless(...) list_for_each_entry(__VA_ARGS__)
-
 #define list_for_each_entry_safe(p, n, h, field)			\
 	for (p = list_entry((h)->next, typeof(*p), field),		\
 	    n = list_entry((p)->field.next, typeof(*p), field); &(p)->field != (h);\
diff --git a/sys/compat/linuxkpi/common/include/linux/rculist.h b/sys/compat/linuxkpi/common/include/linux/rculist.h
index bff2f7e13184..6c21a6943f98 100644
--- a/sys/compat/linuxkpi/common/include/linux/rculist.h
+++ b/sys/compat/linuxkpi/common/include/linux/rculist.h
@@ -44,6 +44,9 @@
 	     &(pos)->member != (head);					\
 	     pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member))
 
+#define	list_for_each_entry_lockless(pos, head, member) \
+	list_for_each_entry_rcu(pos, head, member)
+
 static inline void
 linux_list_add_rcu(struct list_head *new, struct list_head *prev,
     struct list_head *next)