[Devel] [PATCH RHEL7 COMMIT] lists: convert list.h to use READ/WRITE_ONCE

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1160.99.1.vz7.211.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.99.1.vz7.211.2
------>
commit 894ea4d9527ed7a584635d3887f39fb4aa53a840
Author: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
Date:   Thu Sep 28 21:19:49 2023 +0300

    lists: convert list.h to use READ/WRITE_ONCE
    
    This is based on different commits from newer kernel versions.
    
    https://jira.vzint.dev/browse/PSBM-150648
    Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
---
 include/linux/list.h | 51 +++++++++++++++++++++++++++------------------------
 1 file changed, 27 insertions(+), 24 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index b59d57843f4f..f50c550799d8 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -6,6 +6,7 @@
 #include <linux/poison.h>
 #include <linux/const.h>
 
+#include <asm/barrier.h>
 /*
  * Simple doubly linked list implementation.
  *
@@ -23,8 +24,8 @@
 
 static inline void INIT_LIST_HEAD(struct list_head *list)
 {
-	list->next = list;
-	list->prev = list;
+	WRITE_ONCE(list->next, list);
+	WRITE_ONCE(list->prev, list);
 }
 
 /*
@@ -41,7 +42,7 @@ static inline void __list_add(struct list_head *new,
 	next->prev = new;
 	new->next = next;
 	new->prev = prev;
-	prev->next = new;
+	WRITE_ONCE(prev->next, new);
 }
 #else
 extern void __list_add(struct list_head *new,
@@ -86,7 +87,7 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head)
 static inline void __list_del(struct list_head * prev, struct list_head * next)
 {
 	next->prev = prev;
-	prev->next = next;
+	WRITE_ONCE(prev->next, next);
 }
 
 /**
@@ -208,7 +209,7 @@ static inline int list_is_last(const struct list_head *list,
  */
 static inline int list_empty(const struct list_head *head)
 {
-	return head->next == head;
+	return READ_ONCE(head->next) == head;
 }
 
 /**
@@ -227,7 +228,7 @@ static inline int list_empty(const struct list_head *head)
 static inline int list_empty_careful(const struct list_head *head)
 {
 	struct list_head *next = head->next;
-	return (next == head) && (next == head->prev);
+	return (next == head) && (next == READ_ONCE(head->prev));
 }
 
 /**
@@ -403,9 +404,11 @@ static inline void list_splice_tail_init(struct list_head *list,
  *
  * Note that if the list is empty, it returns NULL.
  */
-#define list_first_entry_or_null(ptr, type, member) \
-	(!list_empty(ptr) ? list_first_entry(ptr, type, member) : NULL)
-
+#define list_first_entry_or_null(ptr, type, member) ({ \
+	struct list_head *head__ = (ptr); \
+	struct list_head *pos__ = READ_ONCE(head__->next); \
+	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
+})
 /**
  * list_next_entry - get the next element in list
  * @pos:	the type * to cursor
@@ -664,16 +667,16 @@ static inline int hlist_unhashed(const struct hlist_node *h)
 
 static inline int hlist_empty(const struct hlist_head *h)
 {
-	return !h->first;
+	return !READ_ONCE(h->first);
 }
 
 static inline void __hlist_del(struct hlist_node *n)
 {
 	struct hlist_node *next = n->next;
 	struct hlist_node **pprev = n->pprev;
-	*pprev = next;
+	WRITE_ONCE(*pprev, next);
 	if (next)
-		next->pprev = pprev;
+		WRITE_ONCE(next->pprev, pprev);
 }
 
 static inline void hlist_del(struct hlist_node *n)
@@ -694,32 +697,32 @@ static inline void hlist_del_init(struct hlist_node *n)
 static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
 {
 	struct hlist_node *first = h->first;
-	n->next = first;
+	WRITE_ONCE(n->next, first);
 	if (first)
-		first->pprev = &n->next;
-	h->first = n;
-	n->pprev = &h->first;
+		WRITE_ONCE(first->pprev, &n->next);
+	WRITE_ONCE(h->first, n);
+	WRITE_ONCE(n->pprev, &h->first);
 }
 
 /* next must be != NULL */
 static inline void hlist_add_before(struct hlist_node *n,
 					struct hlist_node *next)
 {
-	n->pprev = next->pprev;
-	n->next = next;
-	next->pprev = &n->next;
-	*(n->pprev) = n;
+	WRITE_ONCE(n->pprev, next->pprev);
+	WRITE_ONCE(n->next, next);
+	WRITE_ONCE(next->pprev, &n->next);
+	WRITE_ONCE(*(n->pprev), n);
 }
 
 static inline void hlist_add_behind(struct hlist_node *n,
 				    struct hlist_node *prev)
 {
-	n->next = prev->next;
-	prev->next = n;
-	n->pprev = &prev->next;
+	WRITE_ONCE(n->next, prev->next);
+	WRITE_ONCE(prev->next, n);
+	WRITE_ONCE(n->pprev, &prev->next);
 
 	if (n->next)
-		n->next->pprev  = &n->next;
+		WRITE_ONCE(n->next->pprev, &n->next);
 }
 
 /* after that we'll appear to be on some hlist and hlist_del will work */