add READ_ONCE() and WRITE_ONCE()

c/list.h

@@ -10,6 +10,7 @@
 
 #include <stddef.h>
 #include <stdbool.h>
+#include "rwonce.h"
 
 /************ originally in <include/linux/types.h> */
 struct list_head {
@@ -61,7 +62,7 @@ struct hlist_node {
  */
 static inline void INIT_LIST_HEAD(struct list_head *list)
 {
-    list->next = list;
+    WRITE_ONCE(list->next, list);
     list->prev = list;
 }
 
@@ -78,7 +79,7 @@ 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);
 }
 
 /**
@@ -118,7 +119,7 @@ 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);
 }
 
 /*
@@ -284,7 +285,7 @@ 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;
 }
 
 /**
@@ -510,7 +511,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  */
 #define list_first_entry_or_null(ptr, type, member) ({                  \
             struct list_head *head__ = (ptr);                           \
-            struct list_head *pos__ = head__->next;                     \
+            struct list_head *pos__ = READ_ONCE(head__->next);          \
             pos__ != head__ ? list_entry(pos__, type, member) : NULL;   \
         })
 
@@ -786,7 +787,7 @@ static inline int hlist_unhashed(const struct hlist_node *h)
  */
 static inline int hlist_unhashed_lockless(const struct hlist_node *h)
 {
-    return !h->pprev;
+    return !READ_ONCE(h->pprev);
 }
 
 /**
@@ -795,7 +796,7 @@ static inline int hlist_unhashed_lockless(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)
@@ -803,9 +804,9 @@ 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);
 }
 
 /**
@@ -847,11 +848,11 @@ 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;
+        WRITE_ONCE(first->pprev, &n->next);
-    h->first = n;
+    WRITE_ONCE(h->first, n);
-    n->pprev = &h->first;
+    WRITE_ONCE(n->pprev, &h->first);
 }
 
 /**
@@ -862,10 +863,10 @@ static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
 static inline void hlist_add_before(struct hlist_node *n,
 				    struct hlist_node *next)
 {
-    n->pprev    = next->pprev;
+    WRITE_ONCE(n->pprev, next->pprev);
-    n->next     = next;
+    WRITE_ONCE(n->next, next);
-    next->pprev = &n->next;
+    WRITE_ONCE(next->pprev, &n->next);
-    *(n->pprev) = n;
+    WRITE_ONCE(*(n->pprev), n);
 }
 
 /**
@@ -876,12 +877,12 @@ static inline void hlist_add_before(struct hlist_node *n,
 static inline void hlist_add_behind(struct hlist_node *n,
 				    struct hlist_node *prev)
 {
-    n->next = prev->next;
+    WRITE_ONCE(n->next, prev->next);
-    prev->next = n;
+    WRITE_ONCE(prev->next, n);
-    n->pprev = &prev->next;
+    WRITE_ONCE(n->pprev, &prev->next);
 
     if (n->next)
-        n->next->pprev = &n->next;
+        WRITE_ONCE(n->next->pprev, &n->next);
 }
 
 /**

c/rwonce.h

@@ -24,6 +24,9 @@
 #ifndef __BR_RWONCE_H
 #define __BR_RWONCE_H
 
+/************ originally in <include/linux/compiler_types.h> */
+# define __compiletime_error(message) __attribute__((error(message)))
+
 /************ originally in <include/linux/compiler_types.h> */
 /*
  * __unqual_scalar_typeof(x) - Declare an unqualified scalar type, leaving
@@ -52,6 +55,36 @@
 	(sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \
 	 sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
 
+#ifdef __OPTIMIZE__
+# define __compiletime_assert(condition, msg, prefix, suffix)		\
+	do {								\
+		extern void prefix ## suffix(void) __compiletime_error(msg); \
+		if (!(condition))					\
+			prefix ## suffix();				\
+	} while (0)
+#else
+# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
+#endif
+
+#define _compiletime_assert(condition, msg, prefix, suffix) \
+	__compiletime_assert(condition, msg, prefix, suffix)
+
+/**
+ * compiletime_assert - break build and emit msg if condition is false
+ * @condition: a compile-time constant condition to check
+ * @msg:       a message to emit if condition is false
+ *
+ * In tradition of POSIX assert, this macro will break the build if the
+ * supplied condition is *false*, emitting the supplied error message if the
+ * compiler has support to do so.
+ */
+#define compiletime_assert(condition, msg) \
+	_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
+
+#define compiletime_assert_atomic_type(t)				\
+	compiletime_assert(__native_word(t),				\
+		"Need native word sized stores/loads for atomicity.")
+
 /************ originally in <asm-generic/rwonce.h> */
 /*
  * Yes, this permits 64-bit accesses on 32-bit architectures. These will