Date: Fri, 25 Sep 2009 09:40:20 -0500 From: Robert Noland <rnoland@FreeBSD.org> To: Ryan Stone <rysto32@gmail.com> Cc: attilio@freebsd.org, hackers@freebsd.org, Fabio Checconi <fabio@freebsd.org> Subject: Re: sx locks and memory barriers Message-ID: <1253889620.2065.12.camel@balrog.2hip.net> In-Reply-To: <bc2d970909250630x3143cbb6k6be2b84e33455ac6@mail.gmail.com> References: <20090924224935.GW473@gandalf.sssup.it> <1253877997.2031.2627.camel@balrog.2hip.net> <bc2d970909250630x3143cbb6k6be2b84e33455ac6@mail.gmail.com>
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On Fri, 2009-09-25 at 09:30 -0400, Ryan Stone wrote: > 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. Ok, then I will sit back and wait for someone with more clue to respond... robert. -- Robert Noland <rnoland@FreeBSD.org> FreeBSD
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