From 9c3cdc1f83a6e07092392ff4aba6466517dbd1d0 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 10 May 2008 19:51:16 -0700 Subject: Move ACCESS_ONCE() to It actually makes much more sense there, and we do tend to need it for non-RCU usage too. Moving it to 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 --- include/linux/compiler.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'include/linux/compiler.h') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index dcae0c8d97e6..c8bd2daf95ec 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 */ -- cgit v1.2.3