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

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Message-ID: <20070809140655.GA17731@shell.boston.redhat.com>
Date:	Thu, 9 Aug 2007 10:06:55 -0400
From:	Chris Snook <csnook@...hat.com>
To:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	torvalds@...ux-foundation.org
Cc:	netdev@...r.kernel.org, akpm@...ux-foundation.org, ak@...e.de,
	heiko.carstens@...ibm.com, davem@...emloft.net,
	schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au,
	wjiang@...ilience.com, cfriesen@...tel.com, zlynx@....org,
	rpjday@...dspring.com, jesper.juhl@...il.com
Subject: [PATCH 16/24] make atomic_read() behave consistently on s390

From: Chris Snook <csnook@...hat.com>

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

Signed-off-by: Chris Snook <csnook@...hat.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)
-
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