[RFC PATCH 4/4] CodeSamples/defer: Add compiler barriers in gettimestampmp.c

[Akira Yokosawa <akiyks@gmail.com>]

From fd5fb9afb6b99b15370a9823b42fa2a92342b92a Mon Sep 17 00:00:00 2001
From: Akira Yokosawa <akiyks@gmail.com>
Date: Sun, 28 May 2017 15:42:45 +0900
Subject: [RFC PATCH 4/4] CodeSamples/defer: Add compiler barriers in gettimestampmp.c

They ensure curtimestamp is read and written once in every
iteration.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
---
 CodeSamples/defer/gettimestampmp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/CodeSamples/defer/gettimestampmp.c b/CodeSamples/defer/gettimestampmp.c
index e794e82..7012caa 100644
--- a/CodeSamples/defer/gettimestampmp.c
+++ b/CodeSamples/defer/gettimestampmp.c
@@ -32,7 +32,7 @@ void *collect_timestamps(void *mask_in)
 	intptr_t mask = (intptr_t)mask_in;

 	while (curtimestamp < MAX_TIMESTAMPS) {
-		while ((curtimestamp & CURTIMESTAMP_MASK) != mask)
+		while ((READ_ONCE(curtimestamp) & CURTIMESTAMP_MASK) != mask)
 			continue;
 		if (curtimestamp >= MAX_TIMESTAMPS)
 			break;
@@ -40,6 +40,7 @@ void *collect_timestamps(void *mask_in)
 		/* Don't need memory barrier -- no other shared vars!!! */

 		ts[curtimestamp++] = get_timestamp();
+		barrier();
 	}
 	smp_mb();
 	return (NULL);
-- 
2.7.4