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authorMark Rutland <mark.rutland@arm.com>2017-10-24 00:07:19 +0300
committerIngo Molnar <mingo@kernel.org>2017-10-25 12:01:00 +0300
commitef4d9af62f47e3070b00c3307a4d8eb5092bb9a2 (patch)
tree9ae149b4fcd4b2d02daaf1e5ac6063c2f2f3b914
parenta9da6f29baf6b61fc94f9768638ee54e9bff173c (diff)
downloadlinux-ef4d9af62f47e3070b00c3307a4d8eb5092bb9a2.tar.xz
locking/atomics, net/average: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_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@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Johannes Berg <johannes@sipsolutions.net> Cc: David S. Miller <davem@davemloft.net> Cc: Johannes Berg <johannes.berg@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-arch@vger.kernel.org Cc: mpe@ellerman.id.au Cc: shuah@kernel.org Cc: snitzer@redhat.com Cc: thor.thayer@linux.intel.com Cc: tj@kernel.org Cc: viro@zeniv.linux.org.uk Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/1508792849-3115-9-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--include/linux/average.h10
1 files changed, 7 insertions, 3 deletions
diff --git a/include/linux/average.h b/include/linux/average.h
index 7ddaf340d2ac..3f462292269c 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/log2.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 */