>From 489b5e3bdeba2f9b733dbe3d85390368dd159174 Mon Sep 17 00:00:00 2001
From: Akira Yokosawa <akiyks@xxxxxxxxx>
Date: Tue, 30 May 2017 20:40:04 +0900
Subject: [RFC PATCH v2 2/2] CodeSamples/defer: Add compiler barriers in gettimestampmp.c
They ensure curtimestamp is read and written once in every
iteration.
[Revised according to Paul's suggestion to use WRITE_ONCE()]
Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx>
---
CodeSamples/defer/gettimestampmp.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/CodeSamples/defer/gettimestampmp.c b/CodeSamples/defer/gettimestampmp.c
index 2abade4..fc5718d 100644
--- a/CodeSamples/defer/gettimestampmp.c
+++ b/CodeSamples/defer/gettimestampmp.c
@@ -32,14 +32,15 @@ void *collect_timestamps(void *mask_in)
long 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;
/* Don't need memory barrier -- no other shared vars!!! */
- ts[curtimestamp++] = get_timestamp();
+ ts[curtimestamp] = get_timestamp();
+ WRITE_ONCE(curtimestamp, curtimestamp + 1);
}
smp_mb();
return (NULL);
--
2.7.4
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