linux-kernel - [PATCH] percpu_counter: __this_cpu_write doesn't need to be protected by spinlock

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Date:	Mon, 1 Jul 2013 10:48:14 +0800
From:	Fan Du <fan.du@...driver.com>
To:	<viro@...iv.linux.org.uk>
CC:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] percpu_counter: __this_cpu_write doesn't need to be protected by spinlock

__this_cpu_write doesn't need to be protected by spinlock, AS we are doing
per cpu write with preempt disabled. And another reason to remove __this_cpu_write
outside of spinlock: __percpu_counter_sum is not a accurate counter.  

Signed-off-by: Fan Du <fan.du@...driver.com>
---
 lib/percpu_counter.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index ba6085d..1fc23a3 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -80,8 +80,8 @@ void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
 	if (count >= batch || count <= -batch) {
 		raw_spin_lock(&fbc->lock);
 		fbc->count += count;
-		__this_cpu_write(*fbc->counters, 0);
 		raw_spin_unlock(&fbc->lock);
+		__this_cpu_write(*fbc->counters, 0);
 	} else {
 		__this_cpu_write(*fbc->counters, count);
 	}
-- 
1.7.1

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