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authorLinus Torvalds <torvalds@linux-foundation.org>2008-05-11 06:51:16 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-05-11 06:51:16 +0400
commit9c3cdc1f83a6e07092392ff4aba6466517dbd1d0 (patch)
tree4dc890f607da4f85ca3a66770e4bce109879e69b /include/linux/compiler.h
parent3ed43c745d2ce0c4ca15ad406285d1cc7e8ceec3 (diff)
downloadlinux-9c3cdc1f83a6e07092392ff4aba6466517dbd1d0.tar.xz
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>
Diffstat (limited to 'include/linux/compiler.h')
-rw-r--r--include/linux/compiler.h12
1 files changed, 12 insertions, 0 deletions
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 */