Move ACCESS_ONCE() to <linux/compiler.h>
It actually makes much more sense there, and we do tend to need it for
non-RCU usage too. Moving it to <linux/compiler.h> will allow some
other cases that have open-coded the same logic to use the same helper
function that RCU has used.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index dcae0c8..c8bd2da 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -182,4 +182,16 @@
# define __section(S) __attribute__ ((__section__(#S)))
#endif
+/*
+ * Prevent the compiler from merging or refetching accesses. The compiler
+ * is also forbidden from reordering successive instances of ACCESS_ONCE(),
+ * but only when the compiler is aware of some particular ordering. One way
+ * to make the compiler aware of ordering is to put the two invocations of
+ * ACCESS_ONCE() in different C statements.
+ *
+ * This macro does absolutely -nothing- to prevent the CPU from reordering,
+ * merging, or refetching absolutely anything at any time.
+ */
+#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
+
#endif /* __LINUX_COMPILER_H */