Date: Fri, 25 Sep 2009 09:30:34 -0400 From: Ryan Stone <rysto32@gmail.com> To: Robert Noland <rnoland@freebsd.org> Cc: attilio@freebsd.org, hackers@freebsd.org, Fabio Checconi <fabio@freebsd.org> Subject: Re: sx locks and memory barriers Message-ID: <bc2d970909250630x3143cbb6k6be2b84e33455ac6@mail.gmail.com> In-Reply-To: <1253877997.2031.2627.camel@balrog.2hip.net> References: <20090924224935.GW473@gandalf.sssup.it> <1253877997.2031.2627.camel@balrog.2hip.net>
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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.
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