Subject: [PATCH 1/24] make atomic_read() behave consistently on alpha

From: Chris Snook <[email-masked]>
Date: Thu, 9 Aug 2007 09:24:42 -0400

From: Chris Snook <[email-masked]>

Purify volatile use for atomic[64]_t on alpha.

Signed-off-by: Chris Snook <[email-masked]>

--- linux-2.6.23-rc2-orig/include/asm-alpha/atomic.h	2007-07-08 19:32:17.000000000 -0400
+++ linux-2.6.23-rc2/include/asm-alpha/atomic.h	2007-08-09 09:19:00.000000000 -0400
@@ -14,18 +14,22 @@

 /*
- * Counter is volatile to make sure gcc doesn't try to be clever
- * and move things around on us. We need to use _exactly_ the address
- * the user gave us, not some alias that contains the same information.
+ * Make sure gcc doesn't try to be clever and move things around
+ * on us. We need to use _exactly_ the address the user gave us,
+ * not some alias that contains the same information.
  */
-typedef struct { volatile int counter; } atomic_t;
-typedef struct { volatile long counter; } atomic64_t;
+typedef struct { int counter; } atomic_t;
+typedef struct { long counter; } atomic64_t;
 
 #define ATOMIC_INIT(i)		( (atomic_t) { (i) } )
 #define ATOMIC64_INIT(i)	( (atomic64_t) { (i) } )
 
-#define atomic_read(v)		((v)->counter + 0)
-#define atomic64_read(v)	((v)->counter + 0)
+/*
+ * Casting to volatile here minimizes the need for barriers,
+ * without having to declare the type itself as volatile.
+ */
+#define atomic_read(v)		(*(volatile int *)&(v)->counter + 0)
+#define atomic64_read(v)	(*(volatile long *)&(v)->counter + 0)
 
 #define atomic_set(v,i)		((v)->counter = (i))
 #define atomic64_set(v,i)	((v)->counter = (i))