linux-kernel - [PATCH 12/46] kref: fix CPU ordering with respect to krefs

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Date:	Fri, 27 Apr 2007 11:53:26 -0700
From:	Greg Kroah-Hartman <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org
Cc:	Oliver Neukum <oneukum@...e.de>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [PATCH 12/46] kref: fix CPU ordering with respect to krefs

From: Oliver Neukum <oneukum@...e.de>

some atomic operations are only atomic, not ordered. Thus a CPU is allowed
to reorder memory references to an object to before the reference is
obtained. This fixes it.

Signed-off-by: Oliver Neukum <oneukum@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 lib/kref.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/lib/kref.c b/lib/kref.c
index 0d07cc3..a6dc3ec 100644
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -21,6 +21,7 @@
 void kref_init(struct kref *kref)
 {
 	atomic_set(&kref->refcount,1);
+	smp_mb();
 }
 
 /**
@@ -31,6 +32,7 @@ void kref_get(struct kref *kref)
 {
 	WARN_ON(!atomic_read(&kref->refcount));
 	atomic_inc(&kref->refcount);
+	smp_mb__after_atomic_inc();
 }
 
 /**
-- 
1.5.1.2

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