atomic_t: Cast to volatile when accessing atomic variables

In preparation for removing volatile from the atomic_t definition, this
patch adds a volatile cast to all the atomic read functions.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/x86/include/asm/atomic64_64.h b/arch/x86/include/asm/atomic64_64.h
index 51c5b40..b014e23 100644
--- a/arch/x86/include/asm/atomic64_64.h
+++ b/arch/x86/include/asm/atomic64_64.h
@@ -18,7 +18,7 @@
  */
 static inline long atomic64_read(const atomic64_t *v)
 {
-	return v->counter;
+	return (*(volatile long *)&(v)->counter);
 }
 
 /**