linux-kernel - [PATCH 09/13] net: average: kill off ACCESS

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Message-Id: <1507573730-8083-10-git-send-email-mark.rutland@arm.com>
Date:   Mon,  9 Oct 2017 19:28:46 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Johannes Berg <johannes.berg@...el.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 09/13] net: average: kill off ACCESS_ONCE()

For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't currently harmful.

However, for some features it is necessary to instrument reads and
writes separately, which is not possible with ACCESS_ONCE(). This
distinction is critical to correct operation.

It's possible to transform the bulk of kernel code using the Coccinelle
script below. However, this doesn't pick up some uses, including those
in <linux/average.h>. As a preparatory step, this patch converts the
file to use {READ,WRITE}_ONCE() consistently.

At the same time, this patch addds missing includes necessary for
{READ,WRITE}_ONCE(), *BUG_ON*(), and ilog2().

----
virtual patch

@ depends on patch @
expression E1, E2;
@@

- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)

@ depends on patch @
expression E;
@@

- ACCESS_ONCE(E)
+ READ_ONCE(E)
----

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Johannes Berg <johannes.berg@...el.com>
Cc: David S. Miller <davem@...emloft.net>
---
 include/linux/average.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/average.h b/include/linux/average.h
index 7ddaf34..7a72de4 100644
--- a/include/linux/average.h
+++ b/include/linux/average.h
@@ -1,6 +1,10 @@
 #ifndef _LINUX_AVERAGE_H
 #define _LINUX_AVERAGE_H
 
+#include <linux/bug.h>
+#include <linux/compiler.h>
+#include <linux/ilog2.h>
+
 /*
  * Exponentially weighted moving average (EWMA)
  *
@@ -48,7 +52,7 @@
 	static inline void ewma_##name##_add(struct ewma_##name *e,	\
 					     unsigned long val)		\
 	{								\
-		unsigned long internal = ACCESS_ONCE(e->internal);	\
+		unsigned long internal = READ_ONCE(e->internal);	\
 		unsigned long weight_rcp = ilog2(_weight_rcp);		\
 		unsigned long precision = _precision;			\
 									\
@@ -57,10 +61,10 @@
 		BUILD_BUG_ON((_precision) > 30);			\
 		BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp);		\
 									\
-		ACCESS_ONCE(e->internal) = internal ?			\
+		WRITE_ONCE(e->internal, internal ?			\
 			(((internal << weight_rcp) - internal) +	\
 				(val << precision)) >> weight_rcp :	\
-			(val << precision);				\
+			(val << precision));				\
 	}
 
 #endif /* _LINUX_AVERAGE_H */
-- 
1.9.1