linux-kernel - [PATCH 1/24] make atomic_read() behave consistently on alpha

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Message-ID: <20070809132442.GA13042@shell.boston.redhat.com>
Date:	Thu, 9 Aug 2007 09:24:42 -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 1/24] make atomic_read() behave consistently on alpha

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

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

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

--- 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))
-
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