Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6

1 files changed, 12 insertions, 0 deletions

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index dcae0c8d97e..c8bd2daf95e 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -182,4 +182,16 @@ extern void __chk_io_ptr(const volatile void __iomem *);
 # 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 */