From owner-freebsd-hackers@FreeBSD.ORG  Fri Sep 25 13:57:02 2009
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Date: Fri, 25 Sep 2009 09:30:34 -0400
Message-ID: <bc2d970909250630x3143cbb6k6be2b84e33455ac6@mail.gmail.com>
From: Ryan Stone <rysto32@gmail.com>
To: Robert Noland <rnoland@freebsd.org>
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Cc: attilio@freebsd.org, hackers@freebsd.org,
	Fabio Checconi <fabio@freebsd.org>
Subject: Re: sx locks and memory barriers
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The code that Fabio proposes looks like this:

sx_slock(&data->lock);
if (data->buffer)
    a = *data->buffer;
sx_sunlock(&data->lock);


This point is that without a memory barrier on the unlock, the CPU is
free to reorder the instructions into the order is his message.