>From 83f496142e594e69f89b154bebcfd8d278ac7831 Mon Sep 17 00:00:00 2001
From: Akira Yokosawa <akiyks@xxxxxxxxx>
Date: Mon, 8 Oct 2018 10:26:24 +0900
Subject: [PATCH 5/5] count: Fix uses of READ/WRITE_ONCE() in count_lim
Add a few READ_ONCE()/WRITE_ONCE()s to prevent load/store tearing
of per-thread variables "counter" and "countermax".
NOTE: Updates of those per-thread variables in utility functions
don't need WRITE_ONCE()s because they are protected by glbcnt_mutex
and can't be seen by read_count().
Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx>
---
CodeSamples/count/count_lim.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/CodeSamples/count/count_lim.c b/CodeSamples/count/count_lim.c
index 69ced9a..c207beb 100644
--- a/CodeSamples/count/count_lim.c
+++ b/CodeSamples/count/count_lim.c
@@ -37,7 +37,7 @@ DEFINE_SPINLOCK(gblcnt_mutex);
static __inline__ int add_count(unsigned long delta) //\lnlbl{add:b}
{
if (countermax - counter >= delta) { //\lnlbl{add:checklocal}
- counter += delta); //\lnlbl{add:add}
+ WRITE_ONCE(counter, counter + delta); //\lnlbl{add:add}
return 1; //\lnlbl{add:return:ls}
}
spin_lock(&gblcnt_mutex); //\lnlbl{add:acquire}
@@ -56,7 +56,7 @@ static __inline__ int add_count(unsigned long delta) //\lnlbl{add:b}
static __inline__ int sub_count(unsigned long delta) //\lnlbl{sub:b}
{
if (counter >= delta) { //\lnlbl{sub:checklocal}
- counter -= delta; //\lnlbl{sub:sub}
+ WRITE_ONCE(counter, counter - delta); //\lnlbl{sub:sub}
return 1; //\lnlbl{sub:return:ls}
}
spin_lock(&gblcnt_mutex); //\lnlbl{sub:acquire}
@@ -80,7 +80,7 @@ static __inline__ unsigned long read_count(void) //\lnlbl{read:b}
sum = globalcount; //\lnlbl{read:initsum}
for_each_thread(t) //\lnlbl{read:loop:b}
if (counterp[t] != NULL)
- sum += *counterp[t]; //\lnlbl{read:loop:e}
+ sum += READ_ONCE(*counterp[t]); //\lnlbl{read:loop:e}
spin_unlock(&gblcnt_mutex); //\lnlbl{read:release}
return sum; //\lnlbl{read:return}
} //\lnlbl{read:e}
--
2.7.4
