[PATCH 16/24] make atomic_read() behave consistently on s390

[Chris Snook <csnook@redhat.com>]

From: Chris Snook <csnook@redhat.com>

Make atomic[64]_read() volatile on s390, to ensure memory is actually read
each time.

Signed-off-by: Chris Snook <csnook@redhat.com>

--- linux-2.6.23-rc2-orig/include/asm-s390/atomic.h	2007-08-08 17:48:53.000000000 -0400
+++ linux-2.6.23-rc2/include/asm-s390/atomic.h	2007-08-09 07:18:56.000000000 -0400
@@ -67,7 +67,11 @@ typedef struct {
 
 #endif /* __GNUC__ */
 
-#define atomic_read(v)          ((v)->counter)
+/*
+ * 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)
 #define atomic_set(v,i)         (((v)->counter) = (i))
 
 static __inline__ int atomic_add_return(int i, atomic_t * v)
@@ -182,7 +186,7 @@ typedef struct {
 
 #endif /* __GNUC__ */
 
-#define atomic64_read(v)          ((v)->counter)
+#define atomic64_read(v)          (*(volatile long long *)&(v)->counter)
 #define atomic64_set(v,i)         (((v)->counter) = (i))
 
 static __inline__ long long atomic64_add_return(long long i, atomic64_t * v)