linux-kernel - CPU ordering with respect to krefs

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Message-Id: <200704021447.59476.oneukum@suse.de>
Date:	Mon, 2 Apr 2007 14:47:59 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org
Subject: CPU ordering with respect to krefs

Hi,

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.

	Regards
		Oliver
Signed-off-by: Oliver Neukum <oneukum@...e.de>
------

--- a/lib/kref.c	2007-04-02 14:40:40.000000000 +0200
+++ b/lib/kref.c	2007-04-02 14:40:50.000000000 +0200
@@ -21,6 +21,7 @@
 void kref_init(struct kref *kref)
 {
 	atomic_set(&kref->refcount,1);
+	smp_mb();
 }
 
 /**
@@ -31,6 +32,7 @@
 {
 	WARN_ON(!atomic_read(&kref->refcount));
 	atomic_inc(&kref->refcount);
+	smp_mb__after_atomic_inc();
 }
 
 /**
-
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